How do you get the trim to stay on the sides of the cars?

Most trim is held on with double sided tape. Clean the old adhesive off the the back of the molding and the area of the car where the trim goes. Go to autoparts or paint supply place and get 3M double sided tape. It comes in several widths. Get the one that fits closest to the one you need. Clean the area of the car with some clean rubbing alcohol. Then reatach the molding to the car. Hope this helps.