The past perfect structure is used to make it clear which of two (or more) actions happened first when talking about a sequence of actions.
Form: had + past participle
- I had visited London before I came here.
- You hadn't been to Wales before.
- Had she visited Belfast before she came to Edinburgh?
- Had he made curry before?
- We had watched the film before we came out.
- Had you visited Edinburgh before?
- They hadn't tired haggis before the came to Scotland.