They are not as they both have the same features it just provides a better understanding when using one diagram in conjunction with the other.State machine diagram shows how state of some object or...
State diagram shows the object undergoing a process. It gives a clear picture of the changes in the object's state in this process. e.g: ATM withdraw Card object state: Checking, Approving, Rejecting...
Designing a UML class diagram is very easy. First try to learn the basics before going deep. As you would have already, Object-oriented programming has become thoroughly practiced, and Class diagrams...