There's no real surprise when it comes to the strategy for the King's Indian Defence: storm white's king side, maybe sac a few things, and mate (ideally).
But what does a practitioner of the QID hope to achieve in terms of the opening and long term goals?
1. d4 Nf6 2. c4 e6 3. Nc3 b6
The key ideas for Black in the Queen's Indian Defense is to:
The Queen's Indian Defense can be reached after the moves:
[FEN ""]
1. d4 Nf6 2. c4 e6 3. Nf3 b6
In the Queen's Indian Defense, black is going aim his light-squared bishop and knight at e4 in order to restrain the moves e4 and to prevent d4 to d5.
White's most popular move is 4...g3 in which white aims to complete development on the king side and counter black on the long diagonal.
A key position is reached after the following:
[FEN ""]
1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. g3 Bb7 5. Bg2 Be7 6. O-O O-O 7. Nc3
In the above position, 7...d5 might seem like a logical move, but it is against the spirit of the opening which say's that Black should be waiting for the most opportune moment to make moves like 7...d5 which occupy the center until the timing is just right. Also, after exchanging pawns on d5, black finds himself with 2 problems, the bishop on b7 is blocked in and the c pawn is on an open file and becomes vulnerable to attack. For example, after white plays Bf4 to eye the c pawn, Black would like to move his pawn to c5, but after the following:
[FEN ""]
1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. g3 Bb7 5. Bg2 Be7 6. O-O O-O 7. Nc3 d5 8. cxd5 exd5
9. Bf4 c5 10. dxc5 bxc5
The above leaves Black with a hanging pawn formation. The d and c pawns are extremely vulnerable and if white can quickly generate an attack such as 11. Ne5 generating a third attacker and pinning the pawn. Black may continue 11...Na6 and now white has 12. Nc4 taking advantage of the pin with the mindset of getting his knight to e3, so Black often plays Qd7, but White just plays Na5
Going back to positon after 7. Nc3, we just illustrated that 7...d5 is not a logical move for black, so instead he plays 7...Ne4 directly occupying the e4 square making it impossible for white to play e4 and he wants to use his f pawn to strengthen his hold over the e4 square and he won't block the diagonal of his bishop. After the following:
[FEN ""]
1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. g3 Bb7 5. Bg2 Be7 6. O-O O-O 7. Nc3 Ne4
8. Nxe4 Bxe4 9. Ne1 Bxg2 10. Nxg2 d5
Black is now willing to play d5 because there is not bishop on b7 anymore and he can now gain share of the center and the position is about equal, so after 7...Ne4, white often plays 8. Qc2, 8...f5 looks like a natural response, but white plays 9. Ne5 and would black would quickly find himself in trouble after:
[FEN ""]
1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. g3 Bb7 5. Bg2 Be7 6. O-O O-O 7. Nc3 Ne4
8. Qc2 f5 9. Ne5 d6 10. Nxe4 fxe4 11. Bxe4
In the above diagram, black does not have time to capture the knight because of the bishop and queen staring down the diagonal, so instead of 8...f5, black should play 8...Nxc3 9. Qxc3 f5. White still has in mind one other factor to gain an advantage. In addition to still play pawn to e4, he also counts on the fact that blacks e6 pawn will become weak if black plays d6 eventually, so for example:
[FEN ""]
1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. g3 Bb7 5. Bg2 Be7 6. O-O O-O 7. Nc3 Ne4
8. Qc2 Nxc3 9. Qxc3 f5 10. b3 Bf6 11. Bb2 d6 12. Rad1 Qe7 13. Ne1 Bxg2 14. Nxg2 Nd7
15. Qc2.
White is looking for small small initiative based upon the weakness of the e6 pawn, so in the end the fight for e4 is the major theme that holds the entire Queen's Indian together.
The main advantage of the Queen's Indian defense is that it gives a good development to the light squared bishop, otherwise Black's problem piece, along the long diagonal.
Because it involves a "slow" development, it gives White a chance to overreach.
For the above reasons, it was a favorite opening of (then) World Champion, J.R. Capablanca (nearly a century ago).
3.Nf3 b6. You've included the moves3.Nc3 b6instead, but while this could transpose to a QID, it probably shouldn't, because in this move order Black has done nothing to prevent4.e4. The QID often gets paired with the Nimzo-Indian in repertoires. In response to3.Nc3, the Nimzo comes out via3...Bb4. And when White instead plays3.Nf3(sometimes specifically to avoid the Nimzo), then Black heads into the QID with3...b6.