Mario Kart Tour is the first Mario Kart game to hit Android and iOS. It's a simplified version of Mario Kart which uses either gyroscope controls or touch inputs rather than a traditional controller. Mario Kart Tour is also rather unusual for kart games in that the goal isn't to reach the finish line, but rather to score a certain number of points.
Other than that, it's the same Mario Kart you know and love. You're still racing either offline or online for supremacy, using weapon boxes to dominate the race, and playing as all your favorites from the Super Mario hall of fame.