We use Present Perfect Tense to talk about something that happened in the past and either has consequences in the present or is still true. It is always connected with now. Check this site, it might help you: http://learnenglish.britishcouncil.org/en/english-grammar/verbs/present-tense/present-perfect

We use this tense when we want to talk about unfinished actions that started in the past and continue to the present. Usually we use it to say 'how long' an action or state has continued with 'since' and 'for'. Often, we use stative verbs in this situation: * I have known Karen since 1994. * She has lived in London for three years.

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