We can use Future Simple to give orders. Normally, we use pronoun YOU in this situation. We can also use imperative sentence, or imperative mood for that. More on that here Introduction to Tenses: Imperative Sentence.
You will do what I say!
Giving orders can be done not only using Future Simple. We can use just the verb to give an order. In this case it’s imperative mood and not the Future Simple construction.
Do what I say!
However, we have other uses of Future Simple Tense: