What is the difference between "Futuro Semplice" and "Futuro Anteriore"?

The difference is very simple: Futuro Semplice is used to express actions that have not happened yet and it is formed with the infinitive of the verb plus its ending. Verb "dire", "to say": dir-ò, dir-ai, dir-à, dir-emo, dir-ete, dir-anno. There are exceptions in the infinitive. Futuro Anteriore is a more complex tense and it is less commonly used. It refers to events that have already happened in the future, it is usually used for hypotheses or uncertainties regarding actions happened in the past or in the future. it is usually used when you are not sure whether these actions have happened or will happen. It is formed from the irregular root of auxiliary verbs "essere" and "avere", which are "sar-" and "avr-" plus the future endings mentioned above, followed by the past participle of the verb. For example: By the time I finish eating, the movie will be already finished. / Quando finirò di mangiare, il film sarà già finito (auxiliary verb root "sar-" + third person future ending "à", +past participle of the verb finish, "finito").