Wolfy's is right. The time depends on the types of bugs you're trying to kill.
At work we usually use either 15 or 20 mins at 121C (hitting about 115kpa). We use
these.
Follow Pete's instructions to keep the stuff you're sterilising off the bottom of the pan.
Then just steam it up for about 20 mins, let pressure hit 110kpg (~16psi) at 121C (if you can), once done you can vent it, and she's cooked.
If you want to tell if your job's done, invest in some
Autoclave Tape. There are strips on it which will turn black IF AND ONLY IF, you've hit sufficient conditions for the right length of time. It's a good failsafe to check that you really are sterilising something. Even with $60,000 autoclaves, we still use it. If the strips aren't going black, you need to modify the sterilisaiton method (either get it hotter, increase the pressure, increase the time, etc). That said, if something's wrong.. you could leave it for an hour, and your stuff still wont be sterile. That's why tape is handy.
cheers