depend on how you want it to be.
E.g. you currently using ME account for apple ID, e.g.
xxx@mac.com or
xxx@me.com since I believe ME uses
xxx@mac.com too if you are from .mac time.
So you need to perform a ME to iCloud migration and all your email will be migrated to iCloud.
Then log in to iCloud like logging in to ME.
If your apple ID is not using ME account then tricky. E.g. Apple ID is
xxx@gmail.com when you sign up for iCloud your iCloud log in ID will be
xxx@gmail.com and iCloud will allow you to create a new ME email if you want and you will have a new ME email address but note this ME email address is just iCloud email service it does not replace your default Apple ID which is
xxx@gmail.com