You don't have to activate anything as there isn't onboard graphics available. I would go in and check your power settings before trying to play any games though.
My apologies about not being clear about the types of games I was referencing. Playing something akin to Minesweeper is one thing, but trying to run anything intensive on the battery is not going to be a good experience, plus you run the risk of damaging things. Unfortunately battery technology has not kept pace with advances in laptop equipment and their power requirements.