Apple make it very easy to manage your Apple ID and it is something you should know how to logon onto in case you have to:
- Change any of your details
- Change your email address
- Add 2 factor authentication ( you really should do this )
- Know how many and what devices you are logged into
Your Apple ID is the email address you gave Apple and the password that accompanied it , and you log onto at Manage Your Apple ID .Apple also give you a way to recover your ID and password should you have forgotten it.
More information on the Apple ID can be found here :Manage Your Apple ID