Here you have the modal verbs scheme:
Also, you can listen to your teacher's explanation right here:
And we invite to visit the next links for more explanations:
https://www.youtube.com/watch?v=sWOEFXnSYoc
https://www.youtube.com/watch?v=_BW-8ob18gw
https://www.youtube.com/watch?v=5Dq7lEw7CKM
