From my experience with my GS project:
Let us start with a naked crankshaft. One important thing to note is the oil hole in that crankshaft. This is the left side of the bike with covers, rotor, starter clutch and gear removed.
(http://216.77.188.54/coDataImages/p/Groups/41/41309/folders/180855/1345500oilportincrank.jpg)
The starter gear free wheels on the crankshaft. Here you see it without a starter clutch/rotor assembly.
(http://216.77.188.54/coDataImages/p/Groups/41/41309/folders/180855/1345411startgearoncrankanote.jpg)
When the "Start" button is pressed, the starter electric motor rotates and here is what happens:
(http://216.77.188.54/coDataImages/p/Groups/41/41309/folders/180855/1345414startermovesallcropanote.jpg)
After the engine gets up to speed, it out runs the starter electric motor. Releasing the "Start" button stops the starter motor and the starter gear stops.
(http://216.77.188.54/coDataImages/p/Groups/41/41309/folders/180855/1345417starterstopscrankmovescropanote.jpg)
That is all there is to it. Follow my "Just picked up..." thread for gory details of a starter motor destroyed by a failure in this process.