To make progress or advance. The project is really starting to come on now that we have more resources.
To begin to operate or function. The lights come on automatically when it gets dark.
To appear or become visible. A rash started to come on after she ate the strawberries.
To encourage or urge someone to do something. Come on, you can do it! Just give it one more try.
To start broadcasting or being shown. The news comes on at 6 PM every evening.