My understanding is that it's a dildo intended to be used in a turning motion rather than a thrusting one. There's nothing to really stop you from thrusting, mind, but the textures on juicers seem to be intended to be most effective when the toy is turned in a circle. I think
the idea is to get you to produce a lot of "juice" of your own.
Though juicers usually have handles to facilitate this, and this toy doesn't seem to have one, nor is it labeled a juicer. I don't think it really matters, though. So long as you're not doing anything dangerous, I say you can use any toy in whatever way feels best.