After placing the object on a wall, you can send a active sim to use it or ask to a non-active sim to do so, chosing one of the four base interactions/positions: Standing, Kneeling, Sitting and Bending. All four actions are restricted to Young-Adults, Adults or Elders sims.
When a sim assumes one of the four idle submissive possitions, it will be possible to interact with this sim in different ways. Those interactions will have different outcomes, giving moodlets and overlays depending of what and how many times you perform a interaction. At this moment, the Bending position is the one that is been working on.
For release a sim from the Sentinel, click in the sim and select the option "Get Out", that's a safeword and like any safeword, can be applied by the sim that's performing the interaction. The buff generated will be corresponding to the feeling that sim have using the device at all, and doesn't matter if the sim perfomed any other flexible interaction or not. Flexible interactions can give more buffs but they are related to consequences and the potential buff after being released is related to the feeling in a general way. Kink sims will have a flirty moodlet and vanilla sims will have a fine moodlet. A special group of vanilla sims wil have a embarassed moodlet.
You can define a sim as a kink for this mod with any of the following traits:
Exhibitionist (Wicked Whims)
Slave/Submissive (Ella Noir Flirty Fetishes)
Any Slave Trait (Nisa Wicked Perversions)
Submissive (Your False Hope)
Humiliation Slut (Kritical)
Check link for them in the Recommended section.