I go = present tense I went = past tense I have gone = perfect present tense I have been going = perfect present progressive tense I want = present tense I wanted = past tense I have wanted = perfect present tense I have been wanting = perfect present progressive tense Source: http://www.amazon.com/English-Grammar-Understanding-Evelyn-Altenberg/dp/0521732166/ref=sr_1_1?ie=UTF8&qid=1400791554&sr=8-1&keywords=english+grammar+altenberg

This is something you could look up yourself. http://www.englishpage.com/verbpage/presentperfect.html

cuando expresas una accion que hiciste en el pasado pero que todavia la sigues hacieno ahora, o por lo menos no indicas que ya la has terminado. ejem I have lived in london. he has worked on tv since 1943. formula. sujeto + have + participio . cuando hay un since, for casi siempre es present perfect...