This command shows you a list of all the users that have logged in and out since the creation of the var/log/wtmp file. There are also some parameters you can add which will show you for example when a certain user has logged in and how long he was logged in for.
If you want to see the last 5 logs, just add -5 to the command like this:
last -5
And if you want to see the last 10, add -10.
Another cool thing you can do is if you add -F you can see the login and logout time including the dates.
last -F
There are quite a lot of stuff you can view with this command. If you need to find out more about this command you can run:
last --help