It measures activity.
The stand ring just needs you to move about for at least 1 minute of every hour. I work at a desk and it’s surprising how often I don’t move.
The exercise ring requires 30 mins exercise everyday.
The move ring measures active calories so mine is set on 450 so from the exercise you do it adds them on.
Luckily I’ve got a treadmill in the house so jump on there after work and finish off my rings