Modal verbs are used to express necessity, possibility, permission, or ability.
They modify the meaning of the main verb and are followed by the infinitive form of that verb.
In German, the modal verbs are: dürfen (may), können (can), mögen (like), müssen (must), sollen (should), wollen (want).
Examples
Ich kann Deutsch sprechen.
I can speak German.
Er will nach Hause gehen.
He wants to go home.
Wir müssen das Buch lesen.
We must read the book.