There are three heads in your shoulder. The front head, side head and rear head. By having very large and overly developed side deltoid heads, your shoulders will appear very round and full.
Pressing movements primarily train the front and side deltoid heads. Side laterals isolate the side deltoid head. You are going to want to do a combination of both of those in your shoulder routine. I would start off your workout with things like barbell/dumbell shoulder press and then finish off your workout with things like dumbbell/cable side lateral raises.
Also remember that the side deltoid is a very common injection site. A lot of pro bodybuilders have done thousands of side deltoid injections. This will cause a big build up of scar tissue in the side deltoid which will also make the muscle looker bigger and rounder.