I have written a booklet about i for my students, send me your Email and I will send it to you

Hi, This tense is used when we want to talk about unfinished actions that started in the past and continue to the present. We use it to say 'how long' an action or state has continued with 'since' and 'for'. The link below will help you with this too, providing you with some exercises if you would like to try them: http://www.perfect-english-grammar.com/present-perfect-use.html Hope this helps you.