The only time past subjunctive is currently used in English is in "if" clauses and similar constructions:
If I were in charge, I would change the rules.
And in wishes:
I wish I were in love again.
Many people use the past indicative form of the verb in these constructions:
If I was in charge, I would change the rules.
Note that the past subjunctive is identical in form to the past indicative except for the verb to be, so one could argue that "had" is subjunctive in
If I had a hammer, I would hammer in the morning.
However, this usually isn't analyzed in this manner.
Some grammarians thought that using the name subjunctive for the "if x were ..." construction was confusing, since it doesn't at all like the current uses of the present subjunctive in English, so they decided to start calling it the irrealis mood instead. This has led to much more confusion, as now some people call this construction the "past subjunctive" while others claim that English has no past subjunctive.
Historically, the construction "if x were ..." is a remnant of a much wider use of both the past and present subjunctive in English, and the uses were more similar to those in German and Spanish then the remaining ones are today. For example, Shakespeare used the present subjunctive in many before clauses in ways similar to the way the subjunctive is used in French and Spanish. This usage is now obsolete.