How do I use the subjunctive in French?

The subjunctive is used as a form of the verb to demonstrate uncertainty or express “a need to do something”.
For example: in English we would simply say “You need to be ready by 8 o’clock.” However in French we incorporate the possibility that you may not be ready by 8 o’clock. Therefore, the subjunctive form has to be used due to the uncertainty.
So instead of saying « Il faut que tu est près à 8 heures. » We change the verb into the subjunctive form: « Il faut que tu soit près à 8 heures. »