When a basketball coach gives his team a motivating speech, the players walk away from it feeling full of enthusiasm, inspired to win the game. Motivating means "providing incentive or impelling to action."
Motivating can describe a talk or a force or a message of some kind, and in that case it's an adjective. It can also be used as a verb, as when your friend says, "My belly is so fat, it's motivating me to stop eating so much ice cream."