meaning of 1.e4 d5

I have never understand  the meaning of  that opening.What is the benefits for black?

Idea of the Qa5 mainline:

Black: "I have archieved the pawn break that usually black plays after a ferocious fight around move 20 in exactly 1 move. I will build a position without weaknesses and develop my pieces in total freedom, much more than in a ruy or sicilian. In fact what i will get is a sort of caro kann classical mainline, with the advantage over the caro kann proper that white can't play something like the dangerous advance lines ( 1.e4 d5 2.e5 is lame, i can put the bishop outside the pawn chain as in a caro but i can also play c7-c5 in one go as in a french; white has nothing). So in fact this is an improved caro kann, a subtler move order which sacrifices some time to cut white options."

White: "what he says is true, his structure is solid and his pieces can develop to natural squares, but i will give him no time for that since to force this structure he wasted time and his queen is still somewhat exposed. I have a lead in development and i will use this quickly to gain an advantage". 

Who is right? nobody knows. Most likely the truth is something between the two points of view.

There are plenty of reasons to believe that the scandinavian is a good opening (including the fact that a lot of GMs play it) , and plenty of reasons to believe that it's somewhat inferior. Make up your own mind; for sure black plan is not illogical, but i personally find black position uninspiring. It's a matter of tastes.

You don't have to study any theory while you wait for your opponent to crush you or make a blunder.

Read my post again please. it starts with "ideas of the Qa5 mainline".

The most played varition in the scandinavian (1.e4 d5 2.exd5 Qxd5 3.Nc3 Qa5) is a very close relative of the caro. The two defences are deeply interconnected. There are even some direct traspositions, for example 1.e4 d5 2.exd5 Nf6 3.c4 c6 4.d4 cxd5 5.Nf3 is a trasposition  to the caro kann/panov-botwinnik attack.

The variation you posted is an unusual gambit line of borderline soundness which indeed has nothing in common with the caro. But the usual way to play the scandinavian is very clse to the caro. I mean, using your "logic" one might say that the caro kann has nothing in common with the caro kann because some ususual variations are very different from the mainline...

wait fot an IM or CM to explain

I have done the same as black. After the white pawn captures my black pawn, my black queen would just capture the white pawn. Even though my queen is brought out early. I normally still have good games.  

true, the caro is richer. I guess the scandi player (i'm not a scandi player; i would rather play the caro  if forced to choose between the two) would say that it's rich of extra possibilities for white. Anyway the two openings are foundamentally a different way to imprement the same idea, an early challenge to e4. The comparison between the two is universally accepted, for example nimzowitch in his writings says that the caro kann is an attempt to improve over the scandinavian (he loved the caro and hated the scandinavian). 

Tiviakov's Qd6 still has a caro feeling in the c6 lines; indeed it's hard to say what is the mainline today. Van Wely for example played Qa5 at Corus this year, and it's certainly the classical mainline, but as you say the most fervent scnadinavian player prefers Qd6.

A chess coach once told me that an advantage of the Scandanavian is that Black for the most part plays on his own terms. The coach (about a 2200 player) was on the side that says it's inferior in theory but not in practice, especially at the sub-master level.

Yes, that is very much the point of the scandi: "dear white, i have decided the pawn structure for this game, and it's a nice one for me.You must follow my desires. I will give you a couple of tempi and some space as a compensation. I challenge you to prove me that it's enough to cause trouble."

 what is ur problem?

what if take my queen back to d8?

i already lost time but my queen is not exposed anymore..

sure,i agree..

How many chances has white to prove black that it's enough to cause trouble?Is it worth for black to take those chances and play the scandinavian?

I just wanted to point out that 1. e4 e5 (The Scandinavian) doesn't necessarily have to turn into a modified Caro Kann.  I agree the mainline most certainly has the same theme though.

Since there is a 2600+ GM which feeds his family by using this defence against top class opposition in most games, of course you can make this your main defence to 1.e4 and be sure that your losses will not be because of the opening. That said, it's obvious that white can cause trouble! White is white and causes trouble against every defence you can throw at him. I think it's Petrosian who said that a serious analysis always leads to the conclusion that black is ok but white is preferable.

If you like it, give it a go. Personally speaking i find it too dry for my tastes, and it lack a bit in variety to play the same structure again and again, but others might equally say that this makes very hard for white to surprise you.

IMO white feels a lot of pressure when playing against the scandinavian because black can use the whole board to create threats

   I started playing the Scandinavian/Center Counter years ago, and have had good results with it. I play the 1.e4 d5  2.exd Qxd5 and if 3.Nc3 Qa5 line. When I looked into the defense I did see that black ends up with a Crao-Kann pawn structure. This is my main defense to 1.e4 and I have no plans to change. Black, with his first move, steers the game. White has played early deviations such as 2.e5,  2.Nc3, but these don't present any big probles. If 2.e5, then black can get hes light squared Bishop out right away, or play 2. c5  undermining pawn support of whites e pawn.

    Also, some black players have tried 1.e4 d5 2. exd Qxd5 3. Nc3 Qd6. I haven't tried this line, but it is supposed to be quite playable.

    Many white players don't take the Center Counter seriously and spend their time preparing for the Sicilian.

    Sometimes white will play

    When the black Queen gets chased with Nc3 it does gain a tempo, but black may be able to show that getting his Queen out early is not always a bad thing.

     Anyway, there are strong players that believe this is a solid defense, and if my opponent plays 1.e4, I will reply with d5. The more I play it the more time I can save in tournament games too (as with any opening if you stick with one) on the clock. Switching openings (and defenses) all the time kind of guarantees one won't get real familiar with any one system costing more time on the clock in a tournament game.