My iMac goes online via a Verizon wireless device. I don't know what my "network" is called and how to use it to go online on my iPad 2.
Your iMac can use it's network card to share it's internet access via Internet sharing.
The setup is very fast and simple. Password encryption is supported.
You can define the settings in System Preferences > Sharing:
To get the name of the network your iMac is joining, open System Preferences (which you can do from the Apple menu at the top left of your screen, in the menu bar).
Then choose Network from the System Preferences window (which is near the center of the window on my Lion system). Select "Wi-Fi" on the left of the Network pref pane, and on the right you should see "Network name:" and the name of the wireless network should appear to the right of it.
On the iPad, you will need to launch the Settings application. Select General on the left side of the screen, then choose Network on the right side of the screen. Tap Wi-Fi, and select the network name that matches the network name used on your iMac.