Yes you can have more than one Apple ID and yes, they are tied to different email addresses.
You can log into and out of accounts on your phone, iPad, mac, and appleTV to access the different music, TVshows, movies, etc that you might have purchased using different IDs.
There was a time when Apple wouldn't let you change your ID associated with iTunes more than once or twice in 90s days but I can't remember the exact scenario when this message would pop up. It might not even matter now that there's no DRM on songs anymore.