Gerunds are verb forms ending in "-ing" that function as nouns. They can be subjects or objects of verbs. Certain verbs, like enjoy and stop, must be followed by a gerund rather than an infinitive. Other verbs, like begin and like, can be followed by either a gerund or infinitive. Gerunds are often used as objects of prepositions.

2. By Miguel Villegas

3.  Gerunds in English correspond in form to
participles (going, swimming, studying, playing,
etc).
 Gerunds, however, are always used as nouns,
as subjects, direct objects of verbs, etc.
Example:
 Swimming is a good exercise.
 He enjoys playing the piano.

4.  Gerunds are ing verbs that are used as nouns. In
these examples, the gerund is the subject of the
sentence:
 Crying can make your eyes red.
 Dancing is a good exercise.
 A gerund phrase can also be used as a noun.
Example:
 Eating chocolate is good for you.
 Smoking cigarettes is bad for you.

5.  Certain verbs in English are always followed by
gerunds and never by infinitives. These verbs are:
enjoy, mind, stop, avoid, consider, finish, deny,
admit, and risk. Example:
 We are considering taking a trip to Chicago.
He has stopped studying English.
 A number of verbs in English may be followed
by either a gerung or an infinitive. The
following verbs are of this group: begin,
continue, like, intend, prefer, hate, etc.

6. Example:
 He likes to study with us.
 He likes studying with us.
 Since gerunds are always used as nouns, they
frequendly used in English as objects of
prepositions. Example:
 Helen is fond of dancing.
 He instisted on going.
 It is a question of finding the right book.