What is the thought process behind this opening move?

why play c4 here? is it just to get a black pawn out of the center? to me, a noob, it just looks like i give a pawn away for free and open up my d4 pawn to an attack from the black queen.

Its a multi-purpose move. First, you are trading a flank pawn for a center pawn, with the hopes youll recapture your lost pawn, and material will be equal. For example, White can play e3 and target that pawn with the light squared bishop. Second, the knight wont have a pawn behind it and the queen is also opened now.

after dxc4 black can play b5 to try and preserve the pawn, I dont know all of the theory but basically its difficult to hang onto the pawn, so white can gambit a pawn. 

yeah, that makes sense. thank you!

i see, you can hog the center and even if black would push their pawn, they would just neglect developing their pieces and white could take with the knight to further strengthen the control of the center and if they don't push, black can still move their knight up. also white can take c4 pawn with the bishop and to counter that black would have to commit way too much on the queen side so it's really not worth it probably.

there is a variation involved in preserving the pawn but most players will just let white recapture the pawn 

if you can undermine a center pawn its usually a good idea, a strong center is really intimidating to play against and its easy to make mistakes, c4 keeps the position sharp and opens lines, the knight can eventually move and the rook can go on c1 too

@1

"why play c4 here?" ++ To undermine black's central pawn d5.
It is interesting to note that 2 c4 is stronger than the developing move 2 Nc3.
Control over the center is even more important than development of pieces into play.

"i give a pawn away for free" ++ Black can take the pawn dxc4, but cannot hold it.
White is then free to play e4 or e3 and recapture Bxc4, developing the bishop.

"open up my d4 pawn to an attack from the black queen" ++ Qd1 defends pawn d4.

It is the life goal of every C pawn to exchange it self for the enemy D pawn whether white or black it doesn't matter, it is only with the attack by the C pawn that the enemy centre can be challenged , this is one of the important principles of positional play, if u don't agree play a game with your C pawn removed and see how difficult it will become to challenge opponent centre control