The United States of America is a union of fifty states and is the third largest country in the world

Negative forms
Отрицательные формы
Depending on the meaning, the negative particle "not" is placed between the auxiliary verb and the main verb (to negate the action of the main verb) or before the gerund (to negate the action of the gerund).
"Not" between the auxiliary verb and the main verb: He did not apologize for losing my book. She doesn't like having to work on Saturdays.
"Not" before the gerund: He was fined for not paying his debt. He apologized for not having written his report on time. I'm surprised at not being asked about it. She is disappointed at not having been invited.

Gerund as subject

Gerunds in the function of the subject can stand alone or be accompanied by dependent words.
Smoking is not allowed here. Курение здесь не разрешено.
Playing guitar is his favorite occupation. Игра на гитаре – его любимое занятие.
Finding them became his main goal. Найти их стало его главной целью.
Reading aloud is very useful for learners of English.
Чтение вслух очень полезно для изучающих английский язык.

Gerund after linking verb BE

Герундий после глагола-связки BE

A gerund after the linking verb BE is used in the function of a predicative noun; that is, a gerund stands in the predicative of the compound nominal predicate.
Seeing is believing. (gerund "seeing" – subject; gerund "believing" – in the function of predicative noun)
Her hobby is writing short stories. Её хобби – написание коротких рассказов.
His favorite occupation is playing guitar. Его любимое занятие – игра на гитаре.

Gerund as direct object

Герундий как прямое дополнение

Gerunds in the function of direct objects are used after many verbs, for example, after "admit, advise, allow, avoid, begin, can't help, continue, deny, discuss, enjoy, finish, forbid, give up, go on, imagine, involve, keep, like, mention, mind, postpone, practice, prefer, quit, recommend, risk, stop, suggest". Examples:
She suggested visiting Venice. Она предложила посетить Венецию.
Stop talking. Begin writing. Go on reading. Keep working.
Прекратите разговаривать. Начинайте писать. Продолжайте читать. Продолжайте работать.