In future tense

In requests

I will be there.

Will you do it for me?

Negative of will

No, I won’t.

To indicate ability

In requests

Informally to ask permission

I can do it.

Can you help me?.

Can I use your phone?

Negative form of can

No, you can’t.

To indicate possibility

To ask permission

I may go to New York.

May I help you?

To indicate past ability

To indicate possibility

In requests

To ask permission

He could play cards well.

I could give you a ride

Could you open the door please?

Could I use your restroom?

Negative past tense

I couldn’t help it.

To express obligation

To conjecture

I should go to the wedding.

He should be in Miami by now.

Negative suggestions

You shouldn’t do that.