I can not use my iCloud and an unknown error occurred when try to use it

You are sign in here .  .  .  with your Apple ID & Password (?).

Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.

You can’t merge multiple Apple ID accounts.

See the following Apple articles:

Sign in to your Apple ID preferences on Mac

Sign in to your Apple ID preferences on Mac – Apple Support (UK)

Set up your Apple ID preferences on Mac

Set up your Apple ID preferences on Mac – Apple Support (UK)

If you can't connect or sign in to iCloud

If you can't connect or sign in to iCloud - Apple Support