Why doesn’t my Apple ID work. I can not sign in on it. There is another Apple ID on it and I need to switch

Click on this link to learn how to 'Sign in with your Apple ID' --> https://support.apple.com/HT204053

If another Apple ID is signed in you may need to enter the password for that ID to sign out of that ID first. If you don't know it or know to whom it belongs you may be in an Activation Lock situation:

'Activation Lock for iPhone, iPad, and iPod touch' is a security feature that's designed to prevent anyone else from using an iPhone, iPad, or iPod touch, if it's ever lost or stolen. To learn more click here --> http://support.apple.com/HT201365

For an individual to remove an activation lock absolutely requires the information for the account that applied the lock. Click on this link to learn 'How to remove Activation Lock' --> https://support.apple.com/HT201441

If you do not know the required information and you are not the original owner, get the owner of the account to remove the lock or return the device for a refund or recycle it. The device is otherwise useless to you. If the owner is unknown and has not provided contact information as a message showing in the login screen, there is no way to contact the owner unless the person who gave you the device knows them.