I'm not entirely sure why the four leaf clover is considered lucky for you when you find it.
But from what I remember learning is that in the early days of Ireland, people in Ireland believed that when they carried the four leaf clover that they would be able to see evil spirits coming and be able to ward them off and/or escape in time.
It's really just a bunch of superstition and there's really no luck to be had when you find a four leaf clover except for the fact that you found the four leaf clover since four leaf Clovers are really rare and you would actually be lucky to find one.