Set the F/Ratio to around F/5.6, and do exposures from any where between 5 minutes to 60 minutes long.
If you are going to do long exposures, make sure it is a moonless night, otherwise the moon washes the photo out.
Constellations with no star trails:
Open the F/Ratio wide open (shown by the smallest number) so the film will gather as much light as possbile in as little time as possible, and do exposures around 20 - 25 seconds long if you are using a 28mm lens. If you are using a 50mm lens, 15 seconds may be the longest you can go with no trails.
Use a 28mm or 50mm lens, and open the F/Ratio open as wide as possible, and do exposures between 10 and 25 seconds long.
OK, so now what do you photograph???
Some good constellations to start with are: Orion, Scorpio, or you can photograph the North or South Celestial Pole (The celestial pole is of course not a constellation!). If you are in the Southern Hemisphere, the Southern Cross is also a nice constellation to photograph!