The target must succeed on a Wisdom saving throw or follow the command on its next turn.
If you were to cast Command as a reaction (e.g. readied action or war caster opportunity) on the turn of the spell's target, does the effect of the spell take place immediately or on the next round?
e.g. If I held the command spell and triggered it once an orc ran around the corner into view and told it to "grovel", would that end the orc's turn there, or would the orc complete it's turn unaffected, only being forced to grovel next round?
Grovel: The target falls prone and then ends its turn.