This slide presentation is going to help you to understand this tense. Look at it very carefully!

[slideshare id=95671&doc=present-perfect-tense71&w=425]

Now it’s time to have further practise:

http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/prperf1.htm

You can go on with the ‘The next exercise’ to have further practise.