There is special group of verbs called modal verbs. These are:

can / could

will / would

shall / should

may / might

must / ought to

They are used in three main ways:

1) To show how likely something is to happen.

I will come.

I might come.

2) To show skills or abilities.

She can play the piano.

He could speak French when he was three.

3) For giving permission, orders and advice.

You must work harder.

May I leave the room, please?