There are two kind of lights....new construction and old construction.....
The new construction lights would go in before you drywall....once drywall is up, you use old construction.
Within each type you also have two different types....Edison socket and pin style fluorescent. The edison will accept a standard incandescent or CFL bulb. The pin style will ONLY take a pin type fluorescent bulb...the ballast is built into the fixture.
That was one of the issues I had in my garage....it was 'supposed' to be the pin style only per code....reason being, if you use the Edison style, someone could go back and replace the CFL's with incandescents.....the inspector cut me some slack because I had all the cans filled with CFL's....and there was a lack in information telling me that it had to be that style of light....now I know....
Which reminds me....I need to talk to HD....they really need to put up a sign telling people that when buying those "new construction" cans that they need to make sure they are following code.