[ENG] Present Perfect

Hello guys, I really need your help here!

I'm an English teacher and today I've got to explain Present Perfect to my students but...

I F*CKING HATE PRESENT PERFECT BECAUSE I CAN'T F*CKING UNDERSTAND IT!

*sighs*

I know how and when to use it, I just don't know how to explain it, how to make them understand it because in Portuguese is different (and I'd rather not ask them to compare both languages).

I appreciate any help!:D