The past perfect tense is composed of a helping verb (had) and the past participle of a verb.

It is used when we are relating two events which happened in the past. It refers to the action that took place first.

The simple past tense of the verb is used for the action that happened later.

• The woman had stood at the gate for half an hour before we noticed her.

• I had sent her a message before she called.

In the above sentences, the verbs had stood and had sent refer to actions that happened first.

The other verbs, noticed and called, refer to actions that happened later.