Let's back up here just a bit, please.
The Time Capsule is already set up.
When you open AirPort Utility and click on the Time Capsule icon, a small window will appear with information about the Time Capsule
Click on Edit in that window and another window will appear with tabs across the top for different functions, in case you need to make a change to the basic setup of the Time Capsule like change the wireless network password, for example.
We are trying to partition the time capsule...
For most folks, that is not possible.
To do that, you would have to open up the Time Capsule case (voiding the warranty)
Pull the hard drive
Install the hard drive in a separate caddy or enclosure
Connect the caddy directly to your Mac
Use Disk Utility to partition the drive
Remove the drive from the caddy
Reinstall the drive in the Time Capsule
Hope it works
Unless you are an experienced technician, and you don't care about the warranty on the Time Capsule, trying to partition the drive would be a very bad idea.