A 2 Gerunds.

A Gerund is a verb when it acts as a noun
gerunds can act as the subject or object of a main verb.
EG: Studying is good for you

Gerunds are used after prepositions, but not usually after 'to'

Gerund Video #1

Gerund Video #2

Subject: Swimming is fun.
Object: I like swimming.
Prepositional object: I read a book about swimming.

Exercise #1

Exercise #2

Exercise # 3

Exercise # 4

Exercise #5