How do I sign on to Appletv

On an actual Apple TV box: go to Settings->Users & Accounts-> Add Account.

Link-> Sign in with your Apple ID on Apple TV - Apple Support

If you have a specific issue, then explain what that is.

On a third party devices with the Apple TV app: Go to the in-app Settings (sprockets wheel icon), then sign in there with your Apple ID account.

Sign in to the Apple TV app - Get started - Apple TV user guide - Apple Support