In the upper left hand corner of the screen you can see your name, your Level number, and a progress bar showing how much experience you need to reach the next Level.
Your Level indicates how far you have progressed in the Beach Buggy Racing League. In higher Levels, the cars are faster. And in addition, the chests you earn from winning races have higher level Powerups in them.
To increase your level, you need to gain experience. You get some experience from winning races, but the best and fastest way to earn experience is to upgrade your Powerups.
Every time you upgrade your Powerups, you earn experience points. If you earn enough experience points, you will increase your Level. To upgrade your Powerups, you need to win and open chests, which will give you Powerup cards. Once you have enough cards your Powerup will be ready to upgrade. Upgrading Powerups makes them more effective against other players.
Gaining experience also unlocks new tracks and new driver and vehicle challenges.