Present Perfect Tense

The structure of the present perfect tense is:

subject	+	auxiliary verb	+	main verb
		have		past participle

Here are some examples of the present perfect tense:

	subject	auxiliary verb		main verb
+	I	have		seen	ET.
+	You	have		eaten	mine.
-	She	has	not	been	to Rome.
-	We	have	not	played	football.
?	Have	you		finished?
?	Have	they		done	it?

Contractions with the present perfect tense

When we use the present perfect tense in speaking, we usually contract the subject and auxiliary verb. We also sometimes do this when we write. 

I have	I've
You have	You've
He has She has It has John has The car has	He's She's It's John's The car's
We have	We've
They have	They've

Here are some examples:

• I've finished my work.
• John's seen ET.
• They've gone home.

by : http://www.englishclub.com/grammar/verb-tenses_present-perfect_s.htm