This is a much harder question to answer than it might appear. In this play, which is an example of "theatre of the absurd", there is much discussion regarding who Godot is really supposed to be.
On the surface, he is a person for whom the characters are waiting, but who never arrives. Some critics of the play have speculated that Becket was playing with the idea of God, and they point to the similarity of the name "Godot" with "God". Man is always searching for God, but he never comes. Or, man is always waiting for someone to make his life better, but this never happens, that "person" never comes.
At the end of the play, Vladimir and Estragon decide to leave, to stop waiting for Godot, but do they go? No. They stay. Nothing happens. It's absurd - theatre of the absurd. Life is absurd. God is existential. If he's there, he doesn't care. And men waste a lot of time in life trying to figure out if he is coming. But he never does. It's up to us to figure out our reason for existence, and if there is a God, he watches with disinterest. Pretty grim philosophy, in my view.
Read the info here on enotes and see what kind of an interpretation YOU can come up with.