Q: How to use my Siri on my iPad?

Siri is not currently available on the iPad (there is only a dictation function) - iOS 6 in the Autumn will add Siri to the current iPad (not the first gen iPad or iPad 2). If you mean dictation then it can be enabled (new iPad only) via Settings > General > Keyboards, and you also need to be online for it to then appear and work on the keyboard.

There is some troubleshooting for FaceTime included on this page : http://support.apple.com/kb/HT4319

Using FaceTime http://support.apple.com/kb/ht4319

Troubleshooting FaceTime http://support.apple.com/kb/TS3367

The Complete Guide to FaceTime: Set-up, Use, and Troubleshooting Problems

http://tinyurl.com/32drz3d

 Cheers, Tom