The subjunctive mood in French is usually used in the present tense to express doubt, necessity, wishes and fear. It is also used for certain set phrases — mainly conjunctions e.g. avant que (before), pour que (in order to/so that), à moins que (unless) and more. It is formed by taking the 3rd person present tense indicative form of the verb (ils/elles), getting rid of the -ent and attaching the subjunctive endings: -e, -es, -e, -ions, -iez, -ent.
There are verbs that take an irregular form in the subjunctive, such as faire, which becomes fass(e/es/e/iez/ionz/ent); savoir, which becomes sach(e/es/e/iez/ion/ent), pouvoir puiss(e/es/e/iez/ions/ent). Here is an example sentence where the subjunctive may be used: ‘Je doute qu’on doive avoir peur du subjonctif.’