Siri was introduced to the iPad with Apple's iOS 6.0 update, but it requires a 3rd generation "iPad 3" in order to work. And because Siri passes your question up to Apple's servers to be analyzed, it also requires an active Internet connection, either through Wi-Fi or a 4G/3G connection.
How to activate Siri on the iPad
First things first, you will need to let your iPad know that you want to ask Siri a question. Similar to the iPhone, you can do this by holding the Home Button down a few seconds.
When activated, Siri will beep at you and open a window on the screen with a small microphone on it. The microphone will have a purple glow to it, indicated Siri is listening. Simply ask a question, and Siri will do her best to comply.
If you want to ask additional questions while the Siri menu is open, simply tap the microphone. It will glow purple again, which means you can ask away. Remember: a purple-glowing microphone means Siri is ready for your question, and a microphone that isn't glowing means she is not listening.
Note: If you have problems getting Siri to activate, make sure you have it turned on in settings. Also, remember it requires an Internet connection and an iPad 3 or later.