1

Modal verbs add specific meaning to the main verb. To talk about ability in the present, we use 'can'. For example, 'I can swim.' To talk about ability in the past, we use 'could'. For example, 'I could swim when I was five.'

2

We also use modals to ask for permission. 'Can' is informal, used with friends and family: 'Can I borrow your pen?' 'Could' is more polite and used with strangers or in formal situations: 'Could I borrow your pen?'

3

'May' is the most formal way to ask for permission, often used with authority figures: 'May I go to the bathroom?' Remember, after any modal verb, always use the base form of the main verb without 'to'.