You attempt to beguile a creature that's visible and within range. If it fails a Wis saving throw, it becomes charmed. If you (or friends) are fighting it, it has advantage on the saving throw. When the target takes dmg, it makes a new Wis saving throw. If successful, the spell ends.
While charmed, you have a telepathic link (if on the same plane). You can use this link to issue commands while you are conscious (no action required). You can specify a simple course of action.
You can use your action to take total control of the target. Until the end of your next turn, the creature takes only the actions you choose. During this time, you can cause the creature to use a reaction, but this requires you to use your own reaction as well.
At Higher Levels. When you cast this spell with a 9th-level spell slot, the duration is concentration, up to 8 hours.