Levels are a gameplay mechanic in Rush Team. Levels are a progression mechanic, players who have played a long time and have earned a lot of experience points have high levels. Every level has its own little badge, what will be displayed right next to your name and will get fancier, the higher your level is. Maximum level achievable is level 100, which no player currently is.
Levels also unlock new weapons for you, the last weapons are unlocked at level 30. Note that VIP and Weapons pack weapons don't have any level requirements on them.