How do I connect my Apple Time Capsule to an existing wireless network?

Hello,
See the Setup Guide for more details.
Connect your Cable/DSL (broadband) modem to the WAN port of your Time Capsule via an Ethernet cable.
Connect the Time Capsule's power cable to an AC outlet.
Open the AirPort Utility. which is located in the Utilities folder, within the Applications folder (/Applications/Utilities).
Thank You.
Apple Router Setup
Apple Time Capsule Setup
Time Capsule Setup