Getting a better understanding of the sicilian defence

After reading some explanations and watching some videos, I started playing the sicilian, but I still want to get a better understanding of it.

- How do I choose a variation? What are the main differences between the classical, the dragon and the Najdorf variation?

- Let's say I finished the development of the defence. What sould I keep in my mind when the game goes on?

Any moves I shouldn't play so I don't weaken the defence?

Any specific areas of the opponent I should target?

- What do I do if the opponent plays an unexpected move in the beginning, like 2.Bc4? Do I stick to the book moves of the sicilian defence, or do I try to take advantage of it?

- One unrelated question:

I always wondered why after 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 black doesn't play e5.

It will kick off the knight, force white to lose tempo and black looks good after that.

Search for pawn structures on wiki, and look at the Sicilian ones.

Black can play e5 there, but it gives white a hole on d5 and the d6 pawn is backwards, and white has an open d file and can get play against this.

I would recommend trying out 1. ...e5 to start out with. But if you have your mind set on the sicilian I would recommend the Kan Variation. It's pretty simple to learn and there is not a lot of theory required. Knowledge of the middlegame positions are more important. 

Many of the questions you asked are specific to certain positions and variations and, in all honesty, would take a while to explain. 

I would guess the easiest way to, for example, learn what to do after 2. Bc4 is to encounter it in a game and post in the forums or look over the game yourself. Not only is it more specific but will stick with you longer as it is your own game.

Best of luck!

To be honest, black doesn't look good.

reason is because of that bishop check and the hole thats why the move a6 is so important i think that the variation you should play should depend on your playing style for example if you are an agressive player i would suggest the dragon , accelerated dragon , hyper accelerated dragon although all sicilians are agresive those 3 are the most agressive i personally started with the hyper accelerated dragon and then played the najdorf 

Here is what to expect from the various Sicilians :

• Dragon : to have fun and play active, but a bit stereotyped
• Najdorf (with ...e5) : quite difficult to handle, but will last a lifetime
• Classical or Scheveninguen : good if you're young and ambitious, and have a stronger player guide you through this structure
• Sveshnikov : easy to play but you need to be dynamic
• Accelerated Dragon : quite positional, more solid
• various ...e6 Sicilian : very strategic and subtle - difficult to play - you need good guidance from stronger players here
• O'Kelly - a good choice to get people out of book

All in all, Sicilian requires a lot of different skills, so the above recommendation to play 1...e5 first is probably a good one

Too bad you don't have diamond membership.  GM Kaidanov recently finished a 3 video series on 2.c3, the Alapin, as an alternative to learning all the mainline theory.  Of course there is a 600 page book  (Sveshnikov ?) available if you want to go deep.   EDIT  Ok, I'm an idiot.  On rereading you want to learn how to play the Sicilian, not against it...

Ok, thanks everyone for helping. I'd like to emphasize the most important question to me that hasn't been answered yet - 

"Let's say I finished the development of the defence. What sould I keep in my mind when the game goes on?

Any moves I shouldn't play so I don't weaken the defence?

Any specific areas of the opponent I should target?"

Black is fine.

And plus, e5 here isnt very common. Usually ppl play it as in the Pelikan, or the Kalakashinov (try saying that three times fast)

I just added that post to show that is is playable, but there ARE better options out there like the Sweshkinov, where you play e5 in better conditions, Kalakashinov, (similar) and other systems where you odnt play e5 at all.

There's a book by David Levy from years ago called 'Sacrifices in the Sicilian', which you can get for free on Scribd. Old, and written in descriptive (!) notation, but if you get through that its a good read in the classic Sicilian games. Will give you a good sense of what Black needs to be careful about in the typical Sicilian structures. More recently I recall David LeMoir wrote something similar more recently, covering sacrifices on b5, d5, e6, f5 and f7. Also the various videos here on pawn structures, if you can afford a couple months diamond membership, are really good.

??? thats not the main line