The subjunctive is a mood used to express statements which are uncertain, for example, expressing emotion, possibility, necessity or desire.
To form the subjunctive for regular verbs (and some irregular ones), take the 3rd person plural 'they' form of the present tense, remove the '-ent' and add the following endings:
I, Je -e
You, Tu -es
He/she/it/one, Il/Elle/On -e
We, Nous -ions
You (PL), Vous -iez
They, Ils/Elles -ent
For example, the verb 'to speak,' parler, is conjugated by taking 'ils parlent', the 'they' form of the present tense, removing the '-ent' leaving 'parl-' and adding the endings:
Je parle, Tu parles, Il parle, Nous parlions, Vous Parliez, Ils parlent
Note that the I, you, he/she, and they forms have the same subjunctive conjugation of 'parler' as the present tense conjugation.