There is no way to passcode lock an app on the stock iPad, only the entire device.
There is a jailbreak tweak that will allow locking apps, but if you are already running an iOS 6 device you'll have to wait. It may be a while until the new jailbreak is out.
For information on jailbreaking check out the sticky tabs in the Hacking section. On the website they are blue threads that stay at the top of the list. On the app they are in a different tab at the top of the list.
To send emails from links on websites (I'm guessing that's what you're trying to do) tap and hold the email link to copy it, then paste it into your favorite email app.