Check whether the steps are the same. It is different to check whether one group has n elements of order n and whether the other group has only n elements of order m. Usually, the second-order number is the most important. For example, Klein has three second orders, and Z4 has only two second orders, so it is different.

All ok's are basically isomorphic. Try to define a bijection so that f(x*y)=f(x)of(y), * and o are two groups of operations respectively.