I was wondering if all the methods defined in the interface MUST be implmented. That means for instance, since I'm not using the create method, I wouldn't have to implement it, just declare it in the data class as requested in the assignment.
No, you are required to give a valid implementation of every method listed in the interface. However, you are not required to actually do anything inside the methods. For example, if one of the methods has a return type void, then all you have to have is an empty body of the method, and that is a valid implementation. If the method has a return type other than void, all you have to do is return a value that is compatible with the return type.