The imperatives of sum/esse (to be) are sg. es/esto and pl. este.
When do we use es? And when esto?
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Es and este are the present imperative, esto and estote are the future imperative. As far as I know, the difference between present and future imperatives is the same for all verbs, and esse is not different.
I think the general differences between present and future imperatives should be asked in a separate question — if not asked already. It is not simply a matter of tense but there are nuances to it.
(The present imperative only has the second person forms. The future one has these and third person forms esto (same as second) and sunto. This is the same for all verbs.)