This is the tricky part, as it is very hard to predict ahead of time what kinds of method your application will require. Therefore, it's usually a good idea to start off with whatever is the norm and then make changes as your applications demand. Going by that, you would end up with an API that looks something like this:
- Push: Pushes an item to the top of the stack
- Pop: Removes an item from the top of the stack
- Peek: Shows the last item pushed into the stack
- Clear: Empties the stack
- Size: Gets the current size of the stack
