What is the imperfect subjunctive and when and how do I use it?

The imperfect subjunctive is a way of expressing something that could have happened, or you wished had happened in the past, or as a way of suggesting something that is unlikely to happen in the future. It isn't used a whole lot in day to day spoken Spanish but it shows to the examiner a deeper understanding of the language, so it's better to be prepared. I can show you ways to put it in your writing and speaking really easily with a few simple phrases. It has 2 sets of verb endings that can be used which we add to the 3rd person plural ("they") stem in the preterite.

For example, let's take the example of 'comer', the 3rd person plural is 'comieron', we take off the '-ron' and then add the endings for imperfect subjunctive which are from 1st person - 3rd person plural: -ra, -ras, -ra, -ramos, -ráis, -ran, or alternatively you can use: -se, -ses, -se, -semos, -séis, -sen. Of course there are exceptions but we can get into that during a session.