The prefix of any @mac.com, @me.com or @icloud.com email are whatever the account holder set them up to be. Apple never assigns anyone an email. Users sign up for one and create the address themselves.
When MobileMe shut down in the fall of 2012, @me.com addresses which had been converted to iCloud accounts before the shutdown became aliases to the iCloud email account. They are no longer independent email accounts, just alias addresses to iCloud email inboxes. See -> iCloud: About your @icloud.com, @me.com, and @mac.com email addresses - Apple Support
If you did not migrate your MobileMe email to iCloud before MobileMe was shut down, then you lost your @me.com email address and it cannot be recovered or used now.
If you have an iCloud account it will be tied to your AppleID. Simply go to https://www.icloud.com and try logging in with your AppleID. If successful, you have an iCloud account and an iCloud email account associated with it. And if your @me.com was migrated to iCloud before the fall of 2012, then that address will simply be an alias address to your iCloud email inbox.