What are the differences between "Simple Past" and "Present Perfect"?

Present Perfect Simple

 

Unfinished actions that started in the past and continue to the present:

• I've known Julie for ten years (and I still know her).

Past Simple

 

Finished actions:

• I knew Julie for ten years (but then she moved away and we lost touch).

In Present Perfect we do not care about the time of the action.Whereas simple past is used when the details of the time or place of an action need to be mentioned. In addition we use simple present when an action is finished and present perfect when we are interested in the results. For instance when you say what did you do at work? You expect an answer dealing with actions. But when you say What have you done at work? you expect to hear the results and the fact that it is a continuation of the working day.

Present perfect has a strong connection with present but simple past has no connection with the present and is finished. This is the simple rule but to understand it in a perfect way the given link will be very helpful.

http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/ppvpast.htm

Simple past is related to a happening in the past which is not related to present. Past perfect, on the other hand, is denoted to something happened in the past and has its effect in present.

The simple past is used to express actions that happen and finish in a specific past time.

The present perfect relates the past with the present. It indicates a completed action in the present time. The action usually starts at some point in the past and continues to the present time. For example: I have written this comment... it means I started writing some point in the past and now the comment is completed as you can see. There is a result!

Simple past finished, while present perfect has recently finished or still has impact

PAST SIMPL SOMTHING ITS NOT INISHED

PRESENT PERFECT SOMETHING ITS FINSHED VERY PERFCT AND  NICE

Past Simple - I worked at that company in - that was and is nit now and does not affect us at any rate

Present Perfect - I have just eaten my dinner and bow am feeling sleepy - it has finished right now, and I feel the effect of it 

 Simple past finished, while present perfect still has impact in present.