An important mechanic to Forza Horizon is the popularity contest that takes place during the whole game, throughout every race, event, and even just driving around the open world.
The scoring occurs by assigning point values to specific actions such as drifting, near misses, high speeds, etcetera and cashing them into an overall score. Performing these actions in quick succession (within 5 to 6 seconds) adds a 0.1x multiplier to the current combo. At the end of the combo when it cashes, all of the points performed in that combo are multiplied by the multiplier and cashed.
There are also certain awards for performing certain actions in a specific order that are worth usually 1000 points to the combo. A full list of these challenges can be found here.
These points feed into an overall total that determines your popularity at the Horizon festival. The player starts at 150th place, and works their way towards 1st, where a 500 000Cr award awaits them. There are also specific Sponsor Challenges (sponsored by real world companies) that also give cash awards that can be found here.