Infinitives

It is best known as BASE FORM

We use the infinitive without 'to':

1

After the auxiliary verb do, does, did in negative sentences and questions. a) He didn’t say anything. b) Does Tim work with you? c) I don’t believe you. 

2

After modal verbs (will, can, must, should, might, may, etc.)

a) You should come with us. b) I can’t play the guitar.

1

After adjectives.

a) It’s important to arrive early at the station.

2

To express a reason or purpose (why).

a) I went to Madrid to visit some family. b) I need time to study for the exam.

3

After question words.

a) I don’t know what to eat. b) I want to learn how to play the guitar.

4

After some verbs.

a) Don’t forget to call me. b) She seems to be distracted.

Some common verbs that are followed by the infinitive are: decide, forget, help, hope, learn, need, offer, plan, promise, remember, seem, try, want, would like. 

The negative form of the infinitive is not to + verb.

She decided not to enter the competition.

https://test-english.com/grammar-points/a2/infinitives-and-gerunds/