With examples, describe the differences in meaning between the use of SIMPLE PAST and PAST PERFECT structures in English?answer in detail

Simple past is one of the two basic tenses in English
grammar, and it is very common.  Its normal purpose is to refer to an action which was
completed before Now: I ate my sandwich.  I
walked the dog.  The Spanish Armada was
defeated in 1588.   We use it to tell others what we did, we
use it to narrate stories, we use it to transcribe the passage of history, and so
forth.  It is a simple statement of a finished action.

The
past perfect verb form, on the other hand, is used to express a past
action which predates another past action:  When I
had eaten my sandwich, I
walked the dog.  The key is that there must be
two past events occurring at different times which are being related, though they
needn't be in the same sentence.  Simple past need describe only one past
event.

Past perfect is a much less frequently used verb
form.  Though it has a safe refuge in formal writing, it is being replaced by simple
past in many less formal situations where other structures can do its job.  It is not
used so often these days, because language users have found that the order of past
events can just as easily be assigned by using prepositions, for instance
(After I ate my
sandwich, I walked the dog).  With 'after', the sequence of events is clear
enough: first the eating, and then the walking.

Some
grammarians will still insist on using past perfect in sentences like the above, but it
too often appears overly formal in contemporary
writing.

Today, the 'mandatory' uses of the present perfect
are in cases of (1) potential confusion about event order (?
When I ate my sandwich, I walked the
dog-- is the eating and the walking simultaneous or consecutive?) and (2) a
desired emphasis on the precedence of the first event (After
I had already eaten my sandwich, Mother told
me that she was going to order a pizza!-- here the speaker wishes to
emphasize that the sandwich was gone and the stomach was satisfied before the wonderful
vision of the pizza arose).

I have included a link to a
simple exposition of the past perfect verb form below.