Setting up my new iMac

My parents recently bought me a used iMac desktop that the previous owners had factory reset. I dont own any other Apple products and I'm trying to update the iMac and set it up from factory reset. When it asks me to sign in with my Apple ID, it just says that my Apple ID hasn't been used in the App Store yet, but I dont have any other apple products to use the app store eith. How do I fix this??