I have a 2000 audi a6 but don't know how to reprogram the remote and I only have one remote. Please help

 

You can't in your current state. At the very least, you need to get another key cut.

1999 and up A4's have an immobilizer, so I'm assuming your A6 does as well. Unless you buy a Vag-Com from Rosstech, you must take it to the dealer. It MUST be programmed through the car! The series of locking and unlocking to program a key only works for NON-IMMOBILIZER cars!