Chagrin:
The Transistor as Switch section shows setup. Also read the "Connecting a transistor from the output of an IC" for an explanation of what's going on. Heck, read the whole page and you'll be a lot smarter in the endThe current drawn by a laser pointer is very low so pretty much any N-channel transistor you have will work.
Why do I need to use a transistor? If the end result is still the laser being rapidly cycled then what's wrong with just using one of the digi out pins?