You can use it for expressing: ability, permission, request and possibility. Example: Can I come tomorrow?

​​Can

​You can use it for expressing: past ability, polite request, permission and possibility. Example: Could I open the door?

​​Could

Expresses possibility and permission. Example: May I help you? Formal situation.

May

Used to ask for permission and expresses a lower probability.Example: You should eat more fruit. Might I talk to you?

Might

​Modal verbs