ing form ("doing")
or
infinitive form ("to do").

For example, only one of the following sentences is correct.
Which one?

I dislike eating too much.
I dislike to eat too much.

Some verbs can be followed by the -ing form or the infinitive without a big change in meaning:
begin, continue, hate, intend, like, love, prefer, propose, start

It's starting to get dark. (or) It's started to get dark.
I like playing soccer. (or) I like to play soccer.

When Do We Use -ing?

The -ing form is used when the word is the subject of a sentence or clause:

Swimming is good exercise.
Doctors say that smoking is bad for you.

The -ing form is used after a preposition:

I look forward to meeting you.
They left without saying "Goodbye."

The -ing form is used after certain verbs:
- avoid, dislike, enjoy, finish, give up, mind/not mind, practise

I dislike getting up early.
Would you mind opening the window

When Do We Use the Infinitive?

The infinitive form is used after certain verbs:

- forget, help, learn, teach, train
- choose, expect, hope, need, offer, want, would like
- agree, encourage, pretend, promise, recommend
- allow, can/can't afford, decide, manage, mean, refuse

I forgot to close the window.
Mary needs to leave early.
Why are they encouraged to learn English?
We can't afford to take a long holiday.

The infinitive form is always used after adjectives, for example:
- disappointed, glad, happy, pleased, relieved, sad, surprised

I was happy to help them.
She will be delighted to see you.

This includes too + adjective:

The water was too cold to swim in.
Is your coffee too hot to drink?

The infinitive form is used after adjective + enough:

He was strong enough to lift it.
She is rich enough to buy two.