How do I use the subjunctive?

The subjunctive is probably the trickiest part of French grammar! To simplify things, the subjunctive may be used in 3 cases:

After circumstancial phrases:
For example - bien que, pour que, pourvu que, avant que, en attendant que, à moins que (these just need learning!) 

After a relative clause suggesting an exception or a desire - 'C'est le plus beau film que j'aie jamais vu' or 'Je cherche une maison qui soit près de la gare' (in this case, the phrase suggests a desire as opposed to 'j'ai trouve une maison qui est près de la gare' which is a reality)

After assertions of feeling or doubt - Je regrette que, Je doute que, Je suis hereuse que, 

The subjunctive is of course even more complicated that this, however this should just be a guide to get your started. This is just a matter of learning the specific phrases that trigger the subjunctive and then putting them into practice!