You target the armor used in the casting of this spell, you imbue it with magic, and it rises and become an Animated Armor under your control. 

On each of your turns, you can use a bonus action to mentally command any armor you animated with this spell if the creature is within 60 feet of you (if you control multiple creatures, you can command any or all of them at the same time, issuing the same command to each one). You decide what action the armor will take and where it will move during its next turn, or you can issue a general command. If you issue no commands, the creature only defends itself against hostile creatures. Once given an order, the creature continues to follow it until its task is complete.

The armor is under your control for 24 hours, after which it stops obeying any command you've given it. To maintain control of the armor for another 24 hours, you must cast this spell on the creature again before the current 24-hour period ends. This use of the spell reasserts your control over up to two sets of armor you have animated with this spell, rather than animating a new one. You may only have two sets of armor animated with this spell at a time.

At Higher Levels
When you cast this spell using a spell slot of 5th level or higher, you animate or reassert control over one additional set of armor for each slot level above 4th, to a maximum of 4 sets of armor at all times, if you were to animate a 5th set of armor, one random set of animated armor would return back to a nonmagical set of plate amor used for the casting of the spell.