Button that says "Go baby go" is optional.
You'll want a toggle switch to "arm" the system, and a momentary switch to actually turn the nos on and off. You could spend $5.00 at radio shack and get both, or get all fancy and spend $50+.
There are also nitrous controllers if you want to be complicated about it, that automatically turn on the nitrous at a certain rpm, and turn it off at a maximum rpm or when you shift.. But those are like $500ish.