In Doritos Crash Course 2, each level has a Split Path that can be unlocked by apparently purchasing them with collected stars. However, the first level appears to unlock by doing something in the level (can't remember what exactly). Is that first level unlocked just to show you how the Split Path works, and all other levels have to be purchased, or do other levels offer some way in the level to unlock it's Split Path without spending stars?
Stars will play a part in unlocking and progressing through the game's stages. Stars will need to be physically picked up by the player's character. Some stars are one-time pickups while others can be picked up over and over. When collecting stars, the stars eventually award bronze, silver, and gold medals with bronze being awarded for the lower amount of stars, and gold for the higher amount. Players can also spend collected stars to unlock courses and other objects and items of the game. Here's the details from Microsoft's blog with plenty of info on the stars and medals:
Collecting Stars (one time)
Every course has a fixed number of stars to physically pick up, half on the main path, half in split paths (which you purchase with stars). Each of these stars can only be collected once.
Players can collect stars in any game mode, except local multiplayer.
Earning Medals (one time)
Whenever the player earns a medal, he is awarded stars according to the medal type.
Each course has a cycle of missions which, when completed, award the player stars. After completing Mission 1, Mission 2 becomes available; after Mission 2, comes Mission 3 and so on, after which the cycle repeats.
Players can spend stars to unlock courses, unlock split paths and to purchase consumables (Rewinds, Jinxes, Power-ups) and Avatar FX (rainbow trail, smoke swirl, etc.).