grammar

Hai guys... it is really nice to join its forum... anyway, may ask something? I am little bit confused to differentiate about simple present perfect tense and past tense. I just think, both of them are the same for telling the story. For example "I have lost my key" and "I lost my key yesterday" does it mean have different meaning? or could you guys give me another example, so I can understand well. I still don't get the sense in using it though I read the characteristic

thank you very much