The past tense in English is used:

to talk about the past
to talk about hypotheses – things that are imagined rather than true.
for politeness.
There are four past tense forms in English:

Tense Form
Past simple: I worked
Past continuous: I was working
Past perfect: I had worked
Past perfect continuous: I had been working
We use these forms:

to talk about the past:
He worked at McDonald’s. He had worked there since July..
He was working at McDonald’s. He had been working since July.

to refer to the present or future in conditions:
He could get a new job if he really tried.
If Jack was playing they would probably win.

and hypotheses:

It might be dangerous. Suppose they got lost.
I would always help someone who really needed help.

and wishes:

I wish it wasn’t so cold.

In conditions, hypotheses and wishes, if we want to talk about the past, we always use the past perfect:
I would have helped him if he had asked.
It was very dangerous, What if you had got lost?
I wish I hadn’t spent so much money last month.

We can use the past forms to talk about the present in a few polite expressions:
Excuse me, I was wondering if this was the train for York.
I just hoped you would be able to help me.