Actually... When you use "on" after a verb, it means "to continue". Not "to start". Please, drive on = please continue to drive = please, continue driving. The action is not starting, but it started before and it should now continue. Please, go on = please continue. Other examples are: I have to work on and on = I have to continue working and working. Read on = continue reading. "Ahead" means "in front". If you say "go ahead" it means "to go forward". It can be used to mean "walk forward" or "continue your story". I hope this helps.

In another context, "go on" can also mean "to go by means of". For instance, the following dialog: Mark: You are going to Canada this weekend, right? Dan: Yes. Mark: Are you driving there? Dan: I'm not sure yet. Mark: Oh, well you could go by train. Dan: I don't want to go on a train. You could also say "I don't want to go by train." Even still, it also means to come into action of operation. For instance, "The lights go on an hour before sunset." It also means to appear on stage. For instance, "The actress had a snack five minutes before she had to go on."