I have the canon eos 400d digital slr camera. Im still a novice and i need to know what setting to use?

So that i can put the camera on a tripod at night and take a picture of the stars over the longest time possible so that it leaves a trail affect.
i just dont know what setting i would have to use

Please help it would really be apreciated

Bulb exposure ISO 100 and f4 to f9 depending on how bright stars are