how do I set up a time capsule backup on my time capsule

The title to your question and the question itself are different. You can do Time Machine backups to a Time Capsule.. not an Airport Extreme without additional parts.

Airport Extreme and Time Capsule are both Apple routers.. almost identical now.. except the TC has a hard disk built in.

Both of them have USB port and with the Airport Extreme if you want to use it for Time Machine backups (Time Machine is the software backup app built into your Mac), then you must plug in a Mac formatted USB disk.

However this is very slow.. so be warned, this is only really suitable for one or two computers. And is no where near as reliable as the Time Capsule with internal disk.

Check out Tesserax's helpful note on speeds expected.

https://discussions.apple.com/docs/DOC-3395

Beaten by Bob.. again!!

We are confused, because on one hand you ask......"how do a set up a time capsule backup on my time capsule"?......and in the next sentence you ask........"how do I set up a time capsule backup on airport extreme"?

Are you perhaps asking about a Time Machine backup here? Time Machine is software on your Mac that is used to back up the data on the Mac to another hard drive......like a Time Capsule.

Do you have both a Time Capsule and an AirPort Extreme? Which models do you have?

What model of Mac do you have? Which operating system is installed on the Mac?