When to Use the Past Perfect?

The past perfect is used to talk about something that occurred in the past, before another action in the past. In other words, we stress the fact that one action, state or event was completed before a certain point in the past.

Analyse the example below:

When John joined our team we had already completed several important projects.

Both events occurred in the past but we use the past perfect to stress that the projects were completed first.

Have a look at some other examples of the past perfect:

I started the presentation after Ann had arrived.
They hadn’t left the office before the alarm rung.
Had you already seen the film before we went to the cinema yesterday?