I had worked (past perfect)

POSITIVE:  I / They / We / You + HAD + worked / eaten (Past Participle)

He / She / It + HAD + worked / eaten (Past Participle)

NEGATIVE:  I / They / We / You + HAD NOT (hadn’t) + worked / eaten (Past Participle)

He / She / It + HAD NOT (hadn’t) + worked / eaten (Past Participle)

QUESTION:  HAD + I / They / We / You + worked / eaten (Past Participle) ?  HAD + He / She / It + worked / eaten (Past Participle)?  For Example,

I had shopped in that shop before we came home. 

They had studied harder when the teacher arrived. 

I helped him to do the task after I had finished my work. 

They had finished building the house when the owner arrived. 

I came here after you had left.

USES: 

We use the past perfect for a finished action before a second point in the past. 

For example,

When the guests arrived, the party had started. (= first the party started, then the guests arrived.)

I washed the floor when the painter had gone. (= first the painter left, then I washed the floor.) 

I had written articles on various topics before he came. ( first I wrote articles, then he came.) 

Something that started in the past and continued up to another action or time in the past. The past perfect tells us ‘how long’, just like the present perfect, but this time the action continues up to a point in the past rather than the present. Usually, we use ‘for + time’. We can also use the past perfect continuous here, so we most often use the past perfect simple with STATIVE VERBS. 

For example,

When he graduated, he had been in Spain for ten years. (= He arrived in Spain ten years before he graduated and lived there until he graduated.)

We use the past perfect to talk about unreal or imaginary things in the past. This is common in the third conditional and after ‘wish’.

For example,

If I had known you were hospitalized, I would have visited you. 

They would have passed the exam if they had studied harder. 

I wish I had asked for her phone number.