Most king pawn players would not expect the move 1...a6!? in response to 1.e4. This move does nothing to claim central squares and it does not develop a piece. This move seems greatly favorable for white since he can now play the excellent move 2.d4. White gains dominance over the center and is not being challenged by black.
Here is one example of a possible move order.
As you can see, white has control of the center and the b7 bishop is nothing white cannot handle. White can castle next move, while black has a ways to go.
Still, black is not too bad in this position. Black will follow up with Nf6 and e6. He will look for breaks such as c5 or d5. If white ever plays e5 to kick the knight, black will play Nf5 and play d6 (main) or f6 (sharper). This is an opening I like to play against passive players who like to develop all their pieces and then attack. Here, black will not lag in development for long and white may be put into a situation that is psychologically uncomfortable.
Here is a tournament game I played using the St George Defense.
Playing both 1.b4 and 1...a6 in the same tournament where you have two hours of thinking and a five second time delay did make me somewhat of a subject in the higher section. If I could win tournament games using unorthodox openings, than I am ready to move up. My opponent did not play 2.d4 and continued with the normal development. This is good, too, but by not playing d4, it guaranteed that I would have a space advantage in the game.
Probably the most famous game using this opening was Karpov v Miles. Miles's victory in the game proved that the opening was playable.
Due to black's first move not immediately countering white in the center, white has many different ideas he can pursue. One idea is to play 2.c4. This prevents 2...b5 unless black gambits the pawn. Black can continue with 2...c5 and after Nf3, 3...g6, and 4.d4, white will have weaknesses on the dark squares and only one central pawn.
Like the Alekhine Defense, white has the option to move his e pawn forward and kick the knight off f6. This can happen immediately on move 5, or most often it happens later when white has safely castled and developed more pieces. In both cases, black will move the knight to d5. Unlike the Alekhine Defense, white will be unable to remove the knight from the centralized square with c4 or Bc4. This will make the knight very strong, and after c5 and Nc6, black will have good counterplay.
Even though black gets a good centralized knight, white still plays e5 to grab extra space, open chances of attacking the black kingside, and allow a white knight to make it to e4.
This is a very common and interesting position in the St George Defense that gives both sides chances. White has a definite space advantage over black. If black does not know what to do and castles king side. This pretty much is a death sentence since white will sacrifice his bishop on h7 and follow up with an easy checkmate. White's dark squared bishop could also attack black's queen on g5 and hopefully trade off dark squared bishops.
Black ideas are to break down the white pawn center on c3, d4, and e5, and launch his own attack before white can position his pieces for an attack. Black wants to show that white overextended himself by playing e5.
I do hope that you understand that this is not a horrible opening and it can be quite good for black. Next time you see someone play 1...a6 in response to 1.e4, you better not roll your eyes and think this will be an easy game.