who is godot? what does he stand for?

There are many interpretations for this. Here is one,

Since "Waiting for Godot" is an allegory written in a heartless modern tone, a theatre-goer naturally rummages through the performance in search of a meaning. It seems fairly certain that Godot stands for God. Those who are loitering by the withered tree are waiting for salvation, which never comes.

The rest of the symbolism is more elusive. But it is not a pose. For Mr. Beckett's drama adumbrates--rather than expresses--an attitude toward man's experience on earth; the pathos, cruelty, comradeship, hope, corruption, filthiness and wonder of human existence. Faith in God has almost vanished. But there is still an illusion of faith flickering around the edges of the drama. It is as though Mr. Beckett sees very little reason for clutching at faith, but is unable to relinquish it entirely.