You go to the Jubilife TV station in Jubilife City. Go up to the counter and the woman will let you Live Draw SDY the lotto ticket.

Your lotto ticket will have 5 numbers on it. Starting from the right, if the numbers on the lotto ticket match the ID of any of you Pokemon, you win a prize. The key is to trade lots of Pokemon with your friends or by using the GTS. Hope this helps!