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Is this is a new time capsule ?
Is your Mac connected to TC network ? If so, how it is connected ? WiFi or Ethernet ?
One more question. Is this the first time you are trying to setup Time Machine ?
You have to do some initial configuration. Lets do this step by steps. Go to Applications folder and open Time Machine application. Or click on Apple menu, select System Preferences and select Time Machine. In Time Machine window, turn it on. Now click "Backup Disk" or " Select Disk" button and do you see the Time Capsule disk in the list ?
If so, select it and select Use Disk.
If that didn't work, then go to Applications > Utilities folder and open Airport Utility. Do you see the Time Capsule in Airport Utility ?
How is it going ? Does the TC disk appear in Time Machine application ?