1) A gerund is a verb in its –ing form, used as a noun.
For example: eating, going, seeing
Gerunds are used:
a) As the subject of a sentence.
Smoking is bad for you.
b) After some verbs, such as: like, hate, enjoy, quit, suggest, dislike, deny
I like cooking. I enjoy fishing.
A good learner’s dictionary will tell you whether a verb is followed by a gerund or not.
c) After prepositions.
I’m interested in buying a computer. I’m scared of walking alone in the dark.
2) The infinitive form of the verb is the original verb. It can be with or without ‘to’.
For example: (to) eat, (to) go, (to) see.
The infinitive form is used:
a) After some verbs, such as; agree, arrange, ask, promise, decide, afford
I agreed to do the work. I arranged to see the doctor, They decided to get married.
A good learner’s dictionary will tell you whether a verb is followed by an infinitive or not.
b) To show the reason why you did something.
Tony went to the post office to pay a bill.
c) After adjectives.
I was surprised to see Erica. I’m pleased to meet you.
3 a) Some verbs can be followed by a gerund or infinitive with NO CHANGE in meaning:
For example: start, begin, hate, like, prefer, continue
She started to cry = She started crying.
I hate watching horror films = I hate to watch horror films.
b) Some verbs can be followed by a gerund or a infinitive, but there is a change in meaning.
For example: try, remember, stop
I tried to get into the house. (Getting into the house is your goal or objective).
I tried climbing through the window. (Climbing through the window is one thing you tried in order to obtain your final objective.)
I stopped cleaning the windows. (I was cleaning the windows and then I stopped).
I stopped to clean the windows. (I was driving, and I stopped driving in order to clean the windows).
I remembered to lock the door. (I remembered, and after that I locked the door).
I remember locking the door. (I remember (now) that I locked the door (in the past)).