The document discusses the present perfect tense in English and its three main uses: to describe experience, change, or a continuing situation. It provides examples of the present perfect tense being used to talk about experiences like seeing a movie multiple times or meeting someone before. The tense can also indicate change, such as there having been many earthquakes in California. It then lists three common uses and provides links for further information on the present perfect tense.

2. FORM
has/have + past participle

6. •I have seen that movie twenty times.
•I think I have met him once before.
•There have been many earthquakes in California.
•People have traveled to the Moon.
•People have not traveled to Mars.
•Have you read the book yet?

7. There are basically three uses for the present
perfect tense:
-experience
-change
-continuing situation

8. http://www.englishpage.com/verbpage/presentperfect.html
https://www.englishclub.com/grammar/verb-tenses_present-perfect_u.htm
http://grammar.ccc.commnet.edu/grammar/tenses/present_perfect_progressive.htm