We use just to express that something happened ‘a short time ago’ or ‘very recently’.
This is how we use just correctly in a sentence:
|Just means 'a short time ago'.
We use just with the present perfect and past perfect tenses (have been, had been, etc.).
We put just between the auxiliary verb and the main verb.
|I'd (I had) just seen him in the corridor.
He's (he has) just been to Spain for his holidays.
I'd (I had) just finished dinner when he came.
|In American English, just is used with the past simple tense.||I just saw him.
He just finished writing a book.