Use "must" to tell people things that they have to do. "Must" is more formal than "have to" and is also stronger. It gives the impression that you are really serious and won't allow anyone to disobey you. Teachers, politicians, and other authority figures use it a lot. It's also common in written instructions, like in the example above. Another example is:

All visitors must present a valid photo I.D. before entering.

This is something that you might read on a sign in the lobby of an office building. It means that you have to show your license, passport, or other ID card to the guard before you can go in.

"Must" is also often used when giving deadlines. When you're doing this, use the phrase, "___ must be ___ed by ___":

All applications must be completed by November 30th.