Lisez comes from the verb "Lire" = "To read"
Lisez is the imperative form (when you order someone to do something)
Ex : "Lisez ce livre !" = "Read this book!"
You can use such form when talking to many persons or formally to a single person.
For a single persons that you know very well (like a friend) you would say "Lis ce livre !" instead.
Regards,