okay, 'choke' is for cold starting(when engine is cold). It works by restricting the air and letting more gas in the cylinder. Once the engine warms up a bit you turn the choke off and away you go.
The older style carbs only had a 'flap' that restricted the air, thereby sucking more gas to enrich the mixture.
Credit to Norman for pic
Now the cns style has its own 'choke circuit' which does the same thing, but more efficiently. Have a look here for more detail of the innards:
So, depending on your tuning, you'll want a little bit or a lot of choke to help get running without having to pedal for three blocks. Once you get to know your motor and how she likes the ambient temperature startup will be a quick matter.
Oh, for tuning and whatnot, search around as there's already 100 threads on the subject.