Can somebody please help me undersand the Sicilian?

First of all , the notation I see everywhere is B20: Sicilian Defense
What does B20 mean? 
Also , please confirm for me if what I have understood so far is correct : even though black responding to e4 with c5 does not allow black to develop any bishop , whereas through e4 white has opened up paths to develop bishops , black counters this advantage by having a strong pawn structure in the center columns , often outnumbering white's center pawns 2:1
Am I right ? If not , why is the Sicilian a strong black opening against e4?
If yes , I have not fully developed the skill to use the 2:1 center pawn majority to the fullest advantage. How do I train to do so ? How do I figure out how to use those two center pawns to gain an edge? So far I have just ended up exchanging them or something and then I am lagging in development 

B20 is the Encyclopedia of Chess Openings (ECO) code for that particular opening.

https://www.365chess.com/eco.php

In my opinion, the main idea of 1...c5 is that is *discourages* White's natural follow-up move of 2. d4 because if White plays 2. d4 he loses a tempo from 2...cxd4 3. Qxd4 Nc6. Now you know why White's favorite 2nd move in the Sicilian is 2. Nf3: Now White can play his desired d4 and not lose a tempo because White's piece in the center is a minor piece (knight) instead of a major piece (queen).

P.S.--

Maybe this is a good opportunity for me to mention some new terminology I've started using to describe how one side tries to get the opponent not to play a certain move:

(1) discourage - leave possible but make disadvantageous

(2) repress - leave possible but make suicidal

(3) prevent - make legally impossible

These three words are in increasing order of strength. Here are some examples:

(1) discourage

After 1. e4 Black wants to make 2. d4 disadvantageous to White, so Black plays 1...c5 so that White will lose a tempo if he plays 2. d4 cxd4 3. Qxd4 Nc6.

(2) repress

After 1. e4, Black wants to make e5 so suicidal that normally White would never even consider it, so Black plays 1...d6 so that 2. e5 meets 2...dxe5.

(3) prevent

After 1. e4, Black wants to make 2. e5 absolutely impossible, so he blocks that pawn from being able to move at all to e5 by playing 1...e5.

B20 is an ECO code given by the Encyclopedia of Chess Openings. The strength of Sicilian is demonstrated by thousands of master games. Many engines, even at big depth, don't consider Sicilian as the strongest opening for black. So, it might be not easy to substantiate its strength theoretically.

Hey Yigor, your rating is very inspirational , I would love to hear your personal take . Would you play the sicilian ? If not , what is your response to e4 ? 
Also can you please give me some tips on using the 2:1 pawn outnumbering in the Sicilian ? 

IM pfren's rating is even more inspirational. Well, personally, I like to experiment and I tried almost everything including Sicilian, of course.

 Hahaha ... I just glanced at my stats here. Most of time on 1. e4 I played 1...a6 (48 times! , 58% of wins) followed by 1...e5 (41 times, 59% of wins) and 1...c5 (15 times, 84% of wins). Wow, it seems that I'm great in Sicilian! LoL

1. Youre not following Opening Principles.

2. Youre hanging pieces.

3. Youre missing simple tacitcs.  

The last thing you need to be working on is openings, and especially the sicilain.  

So what should I be working on?

The basics of each phase of the game

Opening:

Follow the Opening principles:

1.      Control the center squares – d4-e4-d5-e5

2.      Develop your minor pieces toward the center – piece activity is the key

Ø  Complete your development before moving a piece twice or starting an attack.

Ø  Move pieces not pawns.

3.      Castle

4.      Connect your rooks

Ø    By move 12, you should have connected your Rooks, or be about to do so.

Middle game:

When you have completed the Opening Principles, you are now at the middle game.  Now you need to formulate a middle game plan.  The middle game is a very complicated part of a chess game.  A simple way to develop a middle game plan is to perform the following steps.

1.      Scan your opponents 5^th, and 6^th ranks (3^rd, and 4^th if your black)

2.      Look for weak pawns, and or weak squares.

Ø  Weak pawns and squares are Pawns, and squares that cannot be defended by another Pawn.

Ø  Knights are excellent pieces on weak squares.

Ø  When deciding on weak squares, and weak Pawns to attack, the closer to the center the better

End game:

Start with the basics:

1.      Learn basic mates – KQ vs. K, KR vs. K, KRR vs. K

2.      Learn Opposition, and Key Squares

3.      Learn basic King and Pawn endings

Pre Move Checklist

1. Make sure all your pieces are safe.

2. Look for forcing moves: Checks, captures, threats. You want to look at ALL forcing moves (even the bad ones) this will force you look at, and see the entire board.

3. If there are no forcing moves, you then want to remove any of your opponent’s pieces from your side of the board.

4. If your opponent doesn’t have any of his pieces on your side of the board, then you want to improve the position of your least active piece.

5. After each move by your opponent, ask yourself: "What is my opponent trying to do?"

I refuse to dumb it down that much.

this is all said BTW

in a zillion books, video and articles by people that range from Good (1800) to fantastic (IM+)

almost NO ONE says a rank beginner should spend lots of time memorizing openings.

yet far too many people do.

so, being smart about this Might not make you a CHESS god- but its does save you from wasting a lot of time. IMHO.

(cue someone saying that MEMORIZING stuff is important, Even WHEN all the chess authors disagree)

And here we go again.  Time to nail a foot to the floor and run around in circles.  I can hear the stameding of the "Opening memorization" crowd herding on over.

1.e4 c5 is basically meaningless on its own. The game has yet to define itself.

For now, before move 10 or 15, only concern yourself with achieving the opening goals. An opening is successful if you reach move 10 or 15:

1) Without falling behind in development / piece activity
2) Without falling far behind in central space
3) Without an unsafe king

After move 10 or 15, you can ask about general ideas like who is attacking on which side of the board, who wants to use pawns, or knights, and on which squares etc.

 The whole "1.e4 opens two diagonals" is a little misleading. Notice almost always after 1.e4 white is playing 2.Nf3 blocking that queen diagonal the first move's annotation was so proud to report.

I understand that chess moves seem 100% mysterious at first, and that's definitely not fun, but if you want to make sense of the opening as a newer player, definitely the opening principals are the way to go. Explanations like opening diagonals on move 1 may make you feel better, but after a while you'll realize it's not important information.

Where on here do you look to see that?

1.e4 c5 2.Nf3 d6 3.c4 is just an inferior structure though. Hole on d4, but no hole on d5. Black is flexible, easy development, and will have good play with b5 or f5 pawn breaks.

Definitely 3.c4 is playable, but you're basically playing as black at that point.

s

I forgot to say

And e5 is not the only way to avoid a Maroczy. Black can play

1.e4 c5 2.Nf3 d6 3.c4 Bg4

or 3...Nf6 4.Nc3 Bg4

"... For beginning players, [Discovering Chess Openings] will offer an opportunity to start out on the right foot and really get a feel for what is happening on the board. ..." - FM Carsten Hansen (2006)

https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf

"... I won’t try to recommend one [general opening book], but if you find one you like, this should be the first opening book you purchase. ... Once you identify an opening you really like and wish to learn in more depth, then should you pick up a book on a particular opening or variation. Start with ones that explain the opening variations and are not just meant for advanced players. ..." - Dan Heisman (2001)

https://web.archive.org/web/20140626180930/http://www.chesscafe.com/text/heisman06.pdf

"... For players who are beginning to learn about openings and want a good overview of the many lines that constitute the Sicilian complex, [Starting Out: The Sicilian, 2nd Edition] is the answer. ..." - FM Carsten Hansen (2009)

https://web.archive.org/web/20140627122350/http://www.chesscafe.com/text/hansen123.pdf

"[After 1 c4 c5, fundamentally,] there are two options. The first is to carry on with a consistent flank strategy ... The standard method of implementing this plan is 2 Nc3, followed by 3 g3 and 4 Bg2. ... The second option is to ... open the centre by playing d4. This plan is logically introduced by 2 Nf3, ... [After 1 c4 e5,] alternatives to 2 Nc3 are rare and of little theoretical significance. The only other move that has any importance at all is 2 g3 ..." - GM Paul van der Sterren (2009)