|The Share button in the Photos app leads to this menu, from which you can email the photo (in this case an annotation in Skitch)|
So, how do you add an account to the Mail app? Open Settings, then Mail, Contacts, Calendars:
This screen also allows you to delete any accounts you have added. Simply tap the account in question and there is a Delete Account button on the following screen.
To add a new account, tap Add Account. The app makes this simple for us by allowing us to access protocols for common email providers: