its on your keyboard. USUALLY (basic)
Space = start, holds are 1, 2, 3 (4 if you're playing a clubber)
` is cancel (sometimes collect as well depending on manufacturer) C is collect when ` isn't usually.
a lot of games, or release threads in the forum has the keys used in a Notes window that pops up when you load a machine
high tech games with many buttons usually have the first letter as their shortcut so like N would be collect nudges, F would be collect Feature and so one.
it'll take a while, but these are the basic ones that most games use