You'll see il faut... written on signs, in lists of rules and regulations and in instructions on how to make things work.
It's often followed by a verb in the infinitive or dictionary form, ending in -er, -ir, or -re, though sometimes you will see the infinitive on its own:
Il faut finir à huit heures Il faut éteindre la lumière Il ne faut pas sortir Tourner ce bouton
You have to finish at eight
You have to turn the light off
You mustn't go out
Turn this knob
It's also quite usual to hear people using tu and vous with a verb:
Vous tournez à droite Tu tournes à gauche
(You) turn right
(You) turn left
When you're getting someone else to do something, you usually just use the tu or vous verb on its own. This is called the imperative:
Tournez à droite Fermes la porte
Turn right
Close the door
Some common expressions using the imperative include: