Explanation present perfect. Short youtube film.
http://www.youtube.com/v/hgcR9fiJ9Bg
Explanation when to use for and since
https://www.englishclub.com/grammar/verb-tenses_present-perfect_fs.htm
Practice
http://www.eclecticenglish.com/grammar/PresentPerfect1D.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=5876