Can, could, had better, may, might, must, ought, shall, should, will, would.
1- Modal don't take a final -s, even when the subject is she, he, or it
2- Modal are followed immediately by the simple form of a verb..
Correct: She can do it.
Incorrect: She can to do it./ she can does it./ she can did it
3- The only exception is ought, which is folowed by an infinitive( to + the simple form of a verb)
Correct: He ought to go to the meeting.
Phrasal Modals. Pharasal modals are common expresion whose meanings are similar to those of some of the modal auxiliaries.
Be able to is similar to can;
Be going to is similar to will.
Be able to do
Be going to do
Be supposed to do
Have to do
Have got to do