What reverse osmosis does
Water is pushed through a very fine membrane that lets water through and holds back much of what is dissolved in it. What is held back is rinsed to the drain.
It is the stage that goes furthest, which is why it is used for drinking and cooking water rather than the whole house.
Why it goes at the kitchen tap
Showers, laundry and toilets do not need drinking water. Putting reverse osmosis on one faucet keeps the system small and puts the treatment where you actually drink.
The rest of the house is handled by the whole home system.
Tankless or tank
Older systems store treated water in a pressure tank under the sink. A tankless unit makes water as the faucet runs, so the cabinet keeps most of its room.
The faucet sits beside your main tap and does not change how the main tap works.
Looking after it
Filter changes come on a schedule, written into your setup notes when the system goes in.
That is the whole routine. There is no tank to drain and nothing to adjust.