Suivez-moi !
Soyez bien prudents !
On doit porter un casque

Instructions and warnings are given by using the -ez ending of a verb without the vous. Grammatically, this is known as the imperative form.

Tenez ! Hold on!
Suivez-moi ! Follow me!
Faites attention ! Pay attention!

An exception to this general rule is soyez... ! (be... !) which is the imperative form of être.
Il faut also tells you that you have to do something. It never changes, no matter who is talking, and can be translated in English as "you/we must" or "it is necessary to". The following verb is in the infinitive form.

Il faut écouter.
You must listen.
Il faut porter un casque.
You must wear a helmet.

Another way of saying "have to" or "must" is with the verb devoir.
je dois tu dois il/ elle/ on doit,
nous devons vous devez ils/ elles doivent

As with il faut, the verb that follows is in the infinitive form.
On doit porter un casque. We must wear a helmet.
Allez ! Off you go!
Choisissez un niveau. Choose a level.
Payez 10 euros; il faut payer 10 euros. Pay 10 euros; you need to pay 10 euros.