Your Apple ID is the same as your Gmail address because you set it up that way. Except in a few places where you can use a telephone number as your account identifier, Apple uses an email address you designate when you set up an account.
How many accounts do you have? If you wish to delete one, read this support article —> How to delete your Apple Account - Apple Support
Carefully and thoroughly read that article for information about what happens when you delete an Apple Account. For example:
"Make sure that you sign out of all your devices to avoid issues with apps that use your Apple Account or iCloud. After your account is deleted, you can’t sign out of iCloud or turn off Find My iPhone Activation Lock on your devices. If you forget to sign out, you might not be able to use your device when your account is deleted."
There are no "guest" users with an Apple Account. There are guest users on a computer but then you are signing in using a computer account, not an Apple Account. Have a look at this recent thread. Why do I have two Apple ID/iCloud passwor… - Apple Community