If you buy one set, one player can play. Up to four people can play together locally. Each person must have their own Nintendo Switch system, physical Kart, and downloaded game.
The Mario Kart Live: Home Circuit software is available as a free download from the Nintendo eShop.
In each package, the following items are included:
Kart (Mario or Luigi)
(2) Arrow markers
(1) USB charging cable (model number HAC-010)