Present Perfect simple

We use the present perfect simple when we want to talk about actions which started in the past and have continued up to the present. We often use it to show the connection between past and present. Note that we never use a present tense when we say how long a situation has been going on, so there is no exact time expressed when the action happened.

"I have always liked English people."
"She's studied human nature all her life."
"They have had this flat since 2001."

The present perfect is also used for long actions and situations which started in the past and went up on until very recently.

"I've painted two rooms since lunchtime."

The present perfect is often used with expressions of time which refer to a period "up to now": for instance, all this year, all my life, so far, during the 20th century,recently, lately, since, for, already, just, yet, ever, never.

"He hasn't worked for years."
"I've learnt my irregular verbs." (= I know them)

http://inglesesocpidepanxon.blogspot.fr/2012/11/present-perfect-simple.html