FaceTime is Apple’s live video chat client. If you are FaceTiming on a phone, people can reach you simply by typing in your phone number, but if you are using iPad to FaceTime, people will need to type in your email address to contact you.
To add or change the email at which you can be accessed by, go to Settings -> FaceTime. Here, you can add your FaceTime email (Notes: Those with an Apple ID will automatically have that Apple ID associated with your their iPad. You can also have multiple email addresses associated with one device, and multiple devices associated with an email address).
Have fun with your iPad!