How do I dominate in the opening and middlegame?

5.Bb5
This is your "good" bishop. It's not necessarily terrible to trade it off early (some openings do that) but you should have a specific idea in mind. If your goal is to play normal/reasonable moves in the opening and go from there then in this structure put the bishop on e2 or d3.

The "good" bishop is the one on the opposite color as your central pawn(s). It's "good" because it tends to be more mobile than the other bishop.

-

6.Nc3
Another move that isn't technically bad, but you need to play it with a purpose. The knight is blocking your c pawn, but normally you want to move it. The c pawn will go to c3 (to strengthen your center, maybe with kingside ideas later e.g. Ne5, Re1, Bd3, Qf3 etc) or pawn to c4 to undermine black's center and/or play on the queenside. Na4, Rc1, b3, Ba3 type of stuff.

-

7.Bxb5
This is ok if we were a little closer to the middlegame. For example imagine 0-0 and Na4 have already been played. Now you're ready to get some activity on the queenside or at least simply stop c5 from happening and keep c6 backward. However in the game 8.Na5 runs into 8...Qa5. As it is, black can now pressure your center with c5, and get some queenside play for themselves.

-

10...c5
And already your opening result feels not so good, but there are chances for an interesting game, you still have the c4 break and if the queenside becomes messy you can win. The annoying thing is black's structure is solid and you have no targets, meanwhile black can start harassing your queenside pawns right away.

-

20.c3
The move is good, I'm just commenting on the position here... notice black has a simple plan of a5-a4-a3 to gang up on c3... and if you stop this by playing a3 yourself then maybe Nd6-c4 and ganging up on b2.

I'm not a big fan of this knight vs your bishop since your bishop is only a defender and not pressuring anything, but at the same time your c3 knight was not good so Na5-xb6 made sense... so it's a bit subtle, but the position on move 20 is somewhat passive due to your choices on moves 5 and 7. Basically whenever you rush to trade off your best pieces, you're left with less-than-best pieces later in the game.

-

21...Nd6
This is a large gift, allowing you to trade your passive minor piece for their strong knight.

Later, the rook endgame is pretty equal and would be a draw with good play.