When we need to use Past Simple and when Past Perfect?

Question

A problem that I don't understand. Please answer.

Answer 1

Use of Simple Past
- action in the past taking place once, never or several times
Example: He visited his parents every weekend.

- actions in the past taking place one after the other
Example: He came in, took off his coat and sat down.

- action in the past taking place in the middle of another action
Example: When I was having breakfast, the phone suddenly rang.

if sentences type II (If I talked, …)
Example: If I had a lot of money, I would share it with you.

Signal Words of Simple Past
yesterday, 2 minutes ago, in 1990, the other day, last Friday
If-Sentence Type II (If I talked, …)

Use of Past Perfect
action taking place before a certain time in the past
(putting emphasis only on the fact, not the duration)
Example: Before I came here, I had spoken to Jack.

Conditional Sentences Type III (condition that was not given in the past)
Example: If I had seen him, I would have talked to him.

Signal Words
already, just, never, not yet, once, until that day (with reference to the past, not the present)
If-Sentences Type III (If I had talked, …)

Example
I got a low mark on my test.
I studied for only 10 minutes for my test.

What happened first?
I studied ....

What happened afterwards?
I got a low .....

So you can join both sentences like this.
I got a low mark igh interest rate on my credit card because I HAD STUDIED for only .....

Answer 2

Alex's answer is nice different than for permitting you to apply 'that we'd write a grammar attempt'. that's no longer good English. "I without notice remembered that we've been going to have a grammar attempt".

Answer 3

The action was done in the past, but it is or its effects are still in the present time. use have v3 form.
I have broken my bones. (I still am in hospital/bad condition.)