My opponent plays 1.d4, an opening I don't like as black, because I like to open by moving my King's pawn two ranks.

I decided to mirror his move, because I'm not knowledgable about how to counter 1. d4.

He goes for what (I think is called) a gambit. Obviously, he wants control of the center squares.

I accept his gambit, because not doing so seems like he could clutter up the middle with white pawns.

He fires the King pawn, getting great control of the middle at this point.

I mirror the move, for two reasons. First, two slow down his access of the middle with pawns. Firing another pawn, in my opinion, would weaken his defenses, if he tries to attack my King's pawn, with the pawn just right of his King. The second reason for this move, is that capturing my King's pawn with his Queen's pawn, would lead me to capturing his Queen, with mine, and removing his King's castle ability when he takes my queen, giving me a slight advantage.

He apparently sees through the (obvious) dubious queen trade. I think moving his queen up a rank would've been a better move, giving him an even more solid middle game. It seems that he knew my next move would've been to take his Queen's pawn, which would've been deep advancement for my pawn, protected by my Queen. If this is the case, then again, simply moving his pawn up a rank would've probably been a better move.

This move was mostly to put him on the defensive, since up until now, I felt like I was merely reacting to my opponent.

This move works out for me. It keeps his knight pinned, and if he attacks my bishop with his rook's pawn, I'll simply capture his knight; this (in my opinion) will make his Queen-side pawn structure weaker. So my plan is to make him pay for trying to take control of the middle.

His King-pawn is currently defenseless with the pinned knight, so I attack with my knight.