Modal verbs are special verbs that can not be used without accompanying a normal verb. However, -
Modals have present and past forms but are not necessarily used for present or past events.
Modals do not take "-s" in the third person.
We use "not" to make modals negative.
Verbs followed Modals should always be in present simple form.
Some common Modal Verbs: Can, Could, May, Might, Ought to, Shall, Should, Must, Will, Would, Have to e.g. I can swim. You should be here by now. They might not know the answers. He will can go with you.(Wrong) She should studied hard last year. (Wrong)