A) One past action happened before another past action or by a stated time in the past: one past action preceded another past action

I had done my work by 5 o’clock.

I had cleaned my flat before I watched TV.

When I arrived, they had finished lunch.

We felt much safer after Denis had locked all the doors.

He had never flown before.

b) The action happened in the past. The result was also visible in the past.

He had repaired his car. He could drive again.

The flat was empty – everyone had gone out.

He had fixed an old armchair. It looked brand new.

Compare the situations presented above with those of the present perfect tense:

He has repaired his car. Now he can drive again.

The flat is empty – everyone has gone away.

He has fixed an old armchair. Now it looks brand new.