I looked at those. Most of the time we need to lift 2 or more wheels and at different heights. How do you raise 2 wheels at different levels? Seems I rarely need to lift just one wheel or two at the same rate.
So each wheel needs two items to be raised. One item is the smaller, wedge shaped piece. The other item is the longer, rounded (cupped/bowled) piece with the holes. You mate the two pieces together by nesting the long piece on top of the short piece.
The closer to the short piece that you place the long piece, the higher you are lifting that wheel. Said another way, the deeper under the long piece that you place the small wedge, the higher it will lift.
So the closer to the center-line of the assembly that you place the smaller wedge piece, in relation to the long piece, the higher you lift.
I had the same type of leveling blocks provided with a van that I rented once. They were okay. It was a little unnerving to think that if the two pieces somehow slid apart (they are smooth plastic, without any retaining pins or features), the vehicle would drop to the ground.
I didn't stay in one place long enough to really verify whether or not the two pieces would settle overtime and lower the vehicle. I'd imagine that they would, but that it would take a while or a lot of vibration/rocking of the vehicle.
TL;DR - They are adjustable for height and that kit includes the pieces necessary to lift two wheels at heights independent of one another.