Modal Verbs in French
The verbs pouvoir (can, to be able to), vouloir (to want to) and devoir (must, to have to) are what we call verbes modaux in French.
These verbs add a nuance to the action of the verb they precede, whether it be an ability, obligation, will or interdiction to complete the action.
Like all -OIR verbs, pouvoir, vouloir and devoir are irregular in most tenses.
On top of these three modal verbs, you'll also find modal phrases that perform the same function in a sentence, i.e. to modulate the action of the verb they precede. Such phrases include avoir besoin de (to need to), avoir envie de (to feel like), or il faut (must).