If you take on d4 and he takes with the queen, you can attack it with the knight, Nc6 and the queen has to move again, giving you another tempo to move another piece out. This is good for black.
More common is the Smith Morra Gambit, c3 after cxd4 with the idea of giving up the pawn for quick development after dxc4 Nxc3.
c5 doesn't prevent (and isn't meant to prevent) d4. After d4 black captures on d4. White doesn't want to recapture with the queen because then black could develop his knight with tempo (the queen is forced to move a 2nd time).
So almost always white develops his knight to f3 first.
There are many different variations of the Sicilian after 1.e4 c5. Often enough though black uses his open c file and pushes his queenside pawns forward to seek play on the queenside. In many variations black doesn't place a pawn in the center in the opening.
Thanks so much for you replies and help!
@Ap0C552
This is something for now as information and for the future to put into practice in your games.
There are 2 theories of chess regarding control of the center (the center is d4,d5,e4,e5)
1.Classical Opening Theory - Control the center by occupying it with yor pawns and pieces.
2.Hypermodern Opening Theory - Control the center with the power of your pawns and pieces. With this method you do not create targets in the center for your opponent to attack.
In practice both of these opening theories are combined in real games.
There is something important for you to notice about the Sicilian Defense. After the moves: 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6. 5.Nc3 a6. Notice that Black is applying the Hypermodern theory because none of Black's pawns and pieces are occupying any of the central squares. And, White is applying the Classical theory. Notice that White's pawns and pieces are occupying center squares: White's pawn at e4 is occupying then central square e4 and his N is occupying the central square d4.
The perspective that I want to emphasize to you is this opening Is a battle ground of Hypermodern theory vs. Classical theory.
In Sicilian, Black allows White to gain superior developement in order to obtain a better pawn structure. I don't think it's the best approach for a beginner, as you called yourself.
Morphy, as White, sometimes went 1 e4 c5 2 d4 cxd4 3 Nf3 to pick up the pawn in delayed fashion.
I am just learning the sicilian defense. I am a beginner and my friend is similar to me (he is my opponent).
He always opens kings pawn as white. So I thought I would try learning sicilian defense, since it is a strong counter I have heard.
So he moves e4, then I move pawn c5, then he moves pawn d4.
In the tutorial I saw on sicilian, my move to c5 was prvent him moving pawn to d4. But he does anyway and it seems like I don't know how to capitalize on this move.
Should I just take his pawn on d4? Then he takes d4 back with queen, and I have lost all presence in the middle of the board.
Now if I just let him move to d4, and my following move is D6, I feel like he has so much better control of center.