Use Of CAN & COULD

(i) To express possibility.

       Can her statement be true? What could succeed if we worked together.

(ii) To express ability or power.

        I can swin, She could read Quran well  at the age of seven.

(iii) To express Permission.

         Can I go to see a movie? Could I use  your pen?

(iv) To express polite request

         Could I have your book? could you tell me the fact?

(v) To give suggestion
        You could try . You could try him on mobile.

Use of MAY

(i) To express Permission.
      You may use my bat for one match. I came in,Sri 

(ii)To express purpose.
       We eat that we may live.We read that may learn.
(iii)To express a wish.
         May you have the best of luck!May her soul rest in peace.
(iv)To denote possibility.

         "It may rain tonight"He may be elected chairman.
(v)To express prayer.
        May you live long, May God bless

Use Of MIGHT

(i)Past forms of 'may'
        He said that he might come.He might    travel.
(ii)To denote a possibility that is more doubtful than 'may'.
        He might be in the bathroom.The patient might recover.
(iii)To denote a gentle reproach.
         You might tell me the truth.
         Well if you were not well,you might
         have told me this before.
(iv)To denote a suggestion.
         You might consult a doctor.You might solve the problem.

 Use of MUST

(i)Fixed determination.
        I must have it.She must learn chemistry.
(ii)Necessity, Compulsion or Strong moral obligation.
         We must be faithful to our teacher.
          You must do your duty.
(iii) Inevitability.
           A man is born must die.
           The day of Judgement must come.
(iv)Duty
          A soldier must be loyal.A student.
          A student must be obedient.
(v) Prohibition or Command
          Students must not eat in the classroom.
          You must not read like this.

Use of OUGHT TO

(i)To denote strong probability.
          You ought to secure full marks in Maths.
          You ought to be able to reach in time.
(ii)To denote duty.
          We ought to love our country.
          We ought not to walk bare foot.
(iii)To express obligation.
           There ought to be more buses during the Eid. 

 Use Of SHALL

(i)To denote future action.
          I shall be much obliged you.
          We shall go to Ajmer.
(ii) Shall in the second and third person is used to denote.
(a)A promise.
        We shall have the book tomorrow.
        They shall have holiday tomorrow.
(b)A command.
         Students shall take their own seats.
(c) Determination.
     They shall work hard.
   You shall do what she has told you.
(d)A threat.
    He shall be punished if he does not
     obey them.You shall suffer for this.