This the Pirc Defense, a relative to the king's Indian Defense. White establishes a pawn center on d4 and e4, and black fianchettos with ...g6, hoping to attack white's center from the flank.

Don't check just because you can. It is almost always counterproductive to play Bb5+ in the first few moves. Consider the consequences if black plays 2...c6. Your bishop must move again, so black gets the beneficial 2...c6 for free. The pawns on c6 and d6 control the important b5, c5, d5, e5 squares. When your opponent lets you, play e4 and d4 to control the center. Then your pawns on d4 and e4 control the important c5, d5, e5, f5 squares. So 2.d4 was a better move.

This is the best reply: ...c6 is beneficial for black the in Pirc setups. 2...a6 is illegal because black is in check.

This is the consequence of 2.Bb5+: had you played 2.Bc4 instead, the position would be: which is identical except that black got in ...c6 for free.

While jkarp is right, central pawns are not attacked in the hope of winning them, but to force the opponent to deal with the threat. 3...d5 was better though, when black safely gets a pawn in the center with tempo.

Jkarp is right, don't hang material for no reason.

The e-pawn hangs to 7...Ncxe4.

You're right, but unsafe pieces are not call weaknesses. Weaknesses are either structurally weak pawns that can be effectively attacked, or weak squares.

It depends on how good the diagonal is for your bishop. Here the bishop is looking at his own pawn on b4, which makes it useless.

This creates a hole on d5 where you can put your knight in the middlegame. A hole is a square which can no longer be guarded by a pawn. Here your opponent's c- and e-pawns have advanced too far, creating a hole on d5.

No, Jkarp, a passed pawn is not a far advanced pawn, but a pawn with no pawns between it and the promotion square on that file and on the adjacent files. This is not a good move, because now your b5-pawn is very weak, and your bishop on a3 bites on granite. 9.bxc5 dxc5 would bring a very different position: In this position, your a3-bishop is tying down black's bishop, now blocked by pawns, to the defense of the c5-pawn. Now you have a open b-file for your rooks.

Jkarp: moving one pawn in front of your king shield is fine if the weakened squares (f6, g7, h6) can be guarded, or the opponent cannot take advantage of the weaknesses. By following up ...g6 with ...Bg7, black's king shield is fine. (9...d5 is not safe.)

This is not a 'tactic', which is a way to win material, but a reasonable move, preparing ...Bb7. (This does weaken the light squares, but it cannot be taken advantage of easily.) Jkarp: pushing pawns is good. Pawn moves don't count as development, but if you don't push pawns, your opponent will use his pawns to drive your pieces out of the center. Pawn moves to restrict the enemy pawn center and to open lines for the pieces to come out are necessary, but unnecessary pawn moves are bad. If you push 2 pawns or less, you might not have enough space for your pieces. Pushing 6 pawns or more weakens too much and wastes time.