Present perfect is has/have + past participle. Usually have seen, has been, have met, have not read... it's used to say that an event happened at an unspecified time before now. It does not refer to specific times, such as last week, yesterday, last year; only "at some point in the past". This will probably help you: http://www.englishpage.com/verbpage/presentperfect.html

we use the present perfect to talk about an action which started in the past and continues to the present. example : * May has lived in paris for the last three years. also used present perfect to talk about a past action with a visible result in the present. Example: * I´ve broken my arm. (I can´t write) we use the present perfect to refer to an experience. Example: * Have you ever beeb to London? also we can use the present perfect for an action which happened at an unstated time in the past. The action is more important than the time. Example: *I´ve been to New York three times so far.