The subjunctive is what we call a 'mood', which is a verb form conveying the attitude of the speaker. By now, you'll be used to employing the indicative mood, which we use to convey facts or statements the speaker feels certain about, such as 'Je m'appelle Alice' or 'Il fait beau'. However, when something is not certain and we want to convey an attitude such as hope or apprehension about it, we use the subjunctive instead. In order to use the subjunctive, we need to alter the form of the verb we're using. For example, the present subjunctive conjugation of 'faire' is 'Je fasse, tu fasses, il fasse, nous fassions, vous fassiez, ils fassent'. An example of a sentence using the subjunctive would be 'J'espère qu'il fasse beau'. The use of the subjunctive here conveys that the speaker doesn't know if the weather is nice outside or not, but they hope it is! Don't be put off if this is confusing at first: it's something that confuses even native speakers. Learning useful phrases that take the subjunctive and using them correctly will therefore make your written and spoken French all the more polished.