Hi Mary, 

Here is the Kwiziq lesson on the past subjunctive with some examples of its use -

https://kwiziq.learnfrenchwithalexa.com/revision/grammar/conjugate-verbs-in-le-subjonctif-passe-compose

Also just to add it is not as widely used as the present subjunctive but you will encounter it more frequently in literature.

Hope this helps!