Past Perfect Simple Tense

We use "past perfect" to say that one action happened before another past action.

Let's say:

1) I have a lesson on Zoom at 10:30.

2) I join the link at 10:35, after the lesson starts.

The lesson had started when I clicked on the link.

You can see that there are two things that happened in the past, but one happened before the other.

Look at these examples:

1) The lesson started when I clicked on the link.

In this example, it means that they happened at the same time, or we don't know which happened first.

2) The lesson had started when I clicked on the link.

In this example, we know which action happened before the other.

Well let's look at these two sentences:

1) When I went to the party, everybody left.

This means, nobody likes you, and they left when they saw you.

2) When I went to the party, everybody had left.

This means, nobody was there when you went there.

They were not there when you arrived.

Yes, you can simply say:

After he spent his holiday in Italy, he wanted to learn Italian.

When we use after/before, it helps us understand which action happened first/later.