What is the difference between Past Simple and Past Perfect tenses?
When to use which?

Understandable?

Yes, thank you very much :)

You are welcome! )

We use Past Simple to talk about things we did regularly in the past. And we talk about it in general. For example, I went to school by bus. In Past Perfect, we did something in the past but we finished it at a certain time in the past. For example, I had done my homework when my friend came. That means that you finished doing your homework before your friend came.