If you are in favor of something, that means that you approve of something, somtimes when that "something" is part of a choice of two or more possibilities.
You will hear "all those in favor of the proposal raise your hand" at a meeting. It means that all those people who approve of the proposal should raise their hands.
"Where do you want to go - the beach or the movies?"
"I'm in favor of going to the movies. It looks like it might rain, so the beach is not so good."