"I don't understand how to use the French subjunctive. Could you explain it for me?"

The French subjunctive is important for the written language, but is rarely heard now in spoken French. You should be able to recognise and form it when doing written translations, as the French still place a lot of value on the written form, even if how they speak it has diverged a little now. Forming the subjunctive is relatively easy; I'll run through it now. You take the third person plural ending of the verb, remove the final -ent, and add the following set of endings: -e, -es, -e, -ions, -iez, -ent, according to whether it's first-, second-person etc. This makes it really easy for all -er verbs, as they're exactly the same in the subjunctive! With -ir verbs, it means there'll be an 'isse' sound there - 'ils finissent', take off the -ent, and you get 'je finisse' - and -re verbs change slightly too - 'ils vendent' -> 'je vende'. There are a few irregulars which you'll just have to learn: pouvoir -> je puisse, with the same set of endings ; faire -> je fasse ; être -> je sois. As for using it, you'll only find the French subjunctive in specific phrases, so you'll always be able to recognise when to use it. The main usage is after 'verbs of volition', where you're expressing that you want someone or something else to do something. For example, after 'vouloir que', 'aimer que', 'souhaiter que'. Thus 'je veux que tu le fasses' is 'I want you to do it'. If you're talking about what the subject wants to do, you don't use it - just say 'je veux le faire'. The second main usage is when expressing doubt - 'je ne pense pas que...', 'je doute que...', 'j'ai crains que'. The last main usage is just in a group of certain phrases, for example 'de peur que', 'avant que', 'afin que', 'bien que', 'pour que', 'quoi que', 'à condition que'. As you'll notice, all these three types of usage require 'que' - if there's no 'que', you won't need the subjunctive! Keep these points in mind and you'll do just fine.