Can and must.

CAN means the ability,  possibility and permission to do something.

MUST means necessity, obligation and certainty that something is true.


CAN´T  stands for lack of ability, lack of permission and the certainty that something is impossible.

MUSN'T stands for prohibition.

In this video and in this chart you can have the information about the modal verbs we are studying.

Pay attention to the pronunciation of CAN and CAN'T.

Here you have a lot of exercises  to practice the use of these two modal verbs; this page and this other,