I'm just guessing, but I'll bet "they" is your teacher.
If this is a homework question, those are strictly forbidden on this forum. Posting a "how do I do this " question as you first post is a dead give-away.
However, since you already posted, look up the command "last", "finger", "who" and also "wc".
Please read the FAQs for this site in the future.
Thanks and keep posting, but non-homework questions.