Participles

A participle is a verbal (verb form) which is used as an adjective.

There are three participles that are commonly used as adjective: the present participle(active voice); the past participle (passive voice) and the perfect participle (active voice).

* The present participle always ends in ing
* The past participle usually ends in ed, d, t, n, or en.The past participle of some of the verbs do not have distinctive endings: swum, gone, sung etc.
*The perfect participle is always formed by prefixing the word having to the past participle: having sung, having driven, having seen etc

Consider an example from GMAT Prep SC:

First discovered more than 30 years ago, Lina's sunbird, a four-and-a-half-inch animal found in the Phillippines and that resembles hummingbird, has shimmering metallic colors on its head; a brilliant orange patch, bordered with red tufts, in the center of its breast; and a red eye.

A. found in the Phillippines and that resembles
B. found in the Phillippines and that, resembling
C. found in the Phillippines and resembling
D. that is found in the Phillippines and it resembles
E. that is found in the Phillippines and that, resembling

OA : C

As we know :

Past participle ---- represents
1) a past condition, or
2) the passive voice or
3) a condition done onto the subject

Present participle ---- represents
1) a present condition, or
2) the active voice or
3) a condition performed by the subject

In the given sentence, we can clearly see that for the 1st participial phrase, the action of "found" happened in the past because Lina's sunbird was found more than 30 years ago. Further Lina's sunbird did not do any finding instead they were found by X not mentioned in the sentence so passive voice is right.

The second participial phrase starting with "resembling" implies that the "Lina's sunbird" is still resembling in the present(a present condition), so the use of present participle is better. We cannot say that the Lina's sunbird "resembled" because then this would illogically mean that they no longer resemble the humming bird.

The present and past participles are used to describe the "Lina's sunbird", they act as adjectives..

For more examples click on the link below:
GMAT Sentence Correction Questions