We use subjonctive when you would use infinitive. Example: I want you to go to the shops for me. Je voudrais que tu AILLES au magasin pour moi. I always teach subjonctive last because it's the less commonly used verb tense (out of the 7 were often use). It's also trickier. At fist I also tought it was archaique but then I realised we use it more than I was giving it credit for. The thing is, if you use a verb of the ER group (example "manger") in the subjonctive form, in a singular person (je, tu, il elle) and the 3rd person plural (ils,elles) then it looks just like the present, so people don't realise it's actually subjonctive. Example : - Je mange une pomme (présent) - Il faut que je mange une pomme (subjonctive). The plurial form (nous, vous) of the ER group looks like imperfect. Example : - Nous mangions un pique-nique quand la tenpête à commencé (imperfect) - Il faut que nous mangions rapidement avant que la tempête ne commence (subjonctive)

The subjunctive is used a lot in French. It's very important to know how to use it and to be able to identify it. The way I learnt it was just to literally learn all the common verbs and conjunctions with take the subjunctive off by heart. The subjunctive is also used after certain conjunctions like: bien que pour que autant que quoique etc. It's also used when your expressing your feeling on something and with verbs of emotion,desire etc, Ex. I am delighted that he is coming home tonight. (You must use the subjunctive here because you are expressing your feeling about a situation the is going to take place) Je suis ravi qu'il revienne chez lui ce soir. My best advice for you would be to check out this website I find it really useful when I need to practice grammar. http://www.francaisfacile.com/cgi2/myexam/liaison.php?liaison=_subjonctif_

Actually, you can make your sentence so you don't use the subjunctive. So you need to know it mostly when you see it. Its use in the end of a sentence after que and verb+que like prefere que.... You must know the verbe être because it's the one we use mostly at this tense. (because french also don't know the others...) Il se peut qu'il soit malade. you could use the conditionnnel: il pourrait être malade. He could be sick