Simple present perfect:
e.g. I have worked
have I worked?
I have not worked
1. We use this to say that something in the past is connected with the present:
"Lemon and Jack have learned some grammar" - They learned it in the past, but still know it NOW.
"The company has opened a new office" - the office was opened last week, and people are working in it NOW
2. It is used to talk about things which have happened several times up to the present:
"Lemon has received 16 emails since breakfast"
or about how long present stuations have lasted:
http://www.learnenglish.org.uk/wordgame_current_frame.html
"Jack has always lived in the same house"
3. You will hear it used for giving news of recent events:
"Cardinal Retzinger has been elected Pope"
Simple Past Perfect:
e.g. I had worked
This is used when we are talking about the past, and then want to refer to something that happened even earlier in the past:
"I suddenly realised I HAD WRITTEN to Jack before"
"Lemon told Jack that she HAD READ the previous thread yesterday"
here are some exercises and games using the simple present perfect and the simple past perfect.
http://www.learnenglish.org.uk/wordgame_current_frame.html
http://www.learnenglish.org.uk/wordgame_current_frame.html
http://www.learnenglish.org.uk/wordgame_current_frame.html
http://www.learnenglish.org.uk/wordgame_current_frame.html