...trying to set up address in imprint...
What do you mean by that? To sign into system Preferences (or Settings)>iCloud you need an Apple ID (which takes the form of an email address) and obviously to know the password. Doing this should set the Mail app up automatically for you.
You should not need to set Mail up manually, but the settings are given here:
If necessary you can reset your password at http://appleid.apple.com