THE -ING FORMS

A verb ending in -ing is either a present participle or a gerund. These two forms look identical. The difference is in their functions in a sentence.

PRESENT PARTICIPLES

A present participle is most commonly used as part of the continuous form of a verb, after verbs of perception, after verbs of movement, or as an adjective.

PRESENT PARTICIPLES AS PART OF THE CONTINUOUS FORM OF A VERB

Present participles are an element in all continuous verb forms (past, present, future, conditional, etc.). The helping verb will indicate the tense, while the present participle remains unchanging.

EXAMPLES

• He is painting.
• She was waiting.
• They will be coming.
• We would be staying.
• I would have been leaving.

PRESENT PARTICIPLES AFTER VERBS OF PERCEPTION

Present participles can be used after verbs of perception in the pattern verb + object + present participle to indicate the action being perceived.

EXAMPLES

• We saw him swimming across the pond.
• I watched her painting Sarah's portrait.
• I couldn't hear her singing because of the noise.
• I would like to see you knitting sometime.

PRESENT PARTICIPLES AFTER VERBS OF MOVEMENT, ACTION, OR POSITION, TO INDICATE PARALLEL ACTIVITY.

EXAMPLES

• She sat looking at the sea.
• He walks reading his newspaper.
• I cook listening to the radio.
• Sally lay listening to the bugs in the grass.

PRESENT PARTICIPLES AS ADJECTIVES

EXAMPLES

• Did you read that amazing book?
• This movie is so exciting!
• His economics class is boring.

Read more about using present participles.

GERUNDS

The gerund always has the same function as a noun, although it looks like a verb. It can be used in the same way as a noun.

A GERUND AS THE SUBJECT OF THE SENTENCE

EXAMPLES

• Eating people is wrong.
• Driving too fast is dangerous.
• Walking is good for you.
• Your knitting it beautiful.

A GERUND AFTER PREPOSITIONS

EXAMPLES

• Can you sneeze without opening your mouth?
• She is good at painting.
• I was the fastest at climbing the rope.
• He learns music by listening to the chords.

A GERUND AFTER CERTAIN SPECIFIC VERBS

EXAMPLES

• I like cooking.
• He enjoys walking.
• They hate milking cows.
• I can imagine drifting away in a balloon.

A GERUND IN COMPOUND NOUNS

EXAMPLES

• I took her to her driving lessons.
• We are going to the swimming pool.
• My uncle does a lot of bird-watching.
• I found this pie by dumpster-diving.

sumber:http://www.ef.com/english-resources/english-grammar/ing-forms/