You have to think opposite from what you are used to when you are e-mailing from the iPad. You have to be in the application that contains the file and open/start an e-mail from there - this is opposite from a "regular" computer where you start in the mail applications and then go get the file. The iPad doesn't share files like a computer.
That said, what is it that you are trying to e-mail? Whatever it is, have that file open in the app. Usually, somewhere in the app is an option to e-mail. Select that option and you'll usually get an e-mail pop-up so you can fill out the mail details. Then, you an send it.
Marilyn