Hello Sally Henz,
Thanks for your question.
Since you might not have actual servers, you can just make up reasonable example numbers.
The idea is to practice using the TCO tool and understand what inputs are needed.
So if you don't have an environment you can find a typical server specs and use as imputs. That will give you an idea for practice.
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola