Герундий (the Gerund) -

-ing form - -ing форма глагола
ing form употребляется:
В роли подлежащего
Exercising is good for your health.

После глаголов:
Admit, appreciate, avoid, consider, continue, deny, fancy, go (for activities), imagine, mind, miss, practise, prevent, quit, save, suggest.
You should avoid eating junk food.

После глаголов
love, like, enjoy, prefer, dislike, hate для выражения общего предпочтения.
Brian prefers walking alone.

После выражений:
be busy, it’s no use, it’s no good, it’s (not) worth, what’s the use of, can’t help, there’s no point (in), can’t stand, have difficulty (in), have trouble etc.
I have difficulty (in) understanding what he says.

После глаголов
Spend, waste, lose (time, money etc.)
He spends an hour playing the guitar every day.

После частицы to c такими глаголами и выражениями, как:
think of, apologise for, object to, look forward to, be used to, in addition to.
She’s looking forward to receiving a letter from him.
I was thinking of calling John
He apologised for being late.

После глаголов prefer
She prefers walking to driving on the way to work

После глаголов
Hear, listen to, notice, see, watch и feel для обозначения незавершенного действия.
I saw Paul waiting for the bus.
(я видел только часть/фрагмент)

НО:
Инфинитив без частицы to употребляется с Hear, listen to, notice, see, watch и feel для обозначения незавершенного действия.
I didn’t see Paul get on the bus. (действие было завершено)

ПРИМЕЧАНИЕ:
Be/get used to+ -ing form
I’m used to working very hard (It’s my habit.)
НО!
I used to work very hard. (I don’t any more)