Every match pays out EXP. EXP only goes up, and as it crosses fixed thresholds your rank rises, from Trainee through the enlisted and officer ranks to the general ranks and, at the very top, Grand Marshal.
Rank is a measure of time played more than skill: it never drops. For skill, look at K/D, win rate and the ranked tier on a player's profile.
OpenCF has seen 102 ranks so far, up to Grand Marshal. The EXP each one needs is listed on the ranks page.
Grand Marshal
Grand Marshal is the highest rank and is shown with its own insignia across the game and on profiles. Look for it on the leaderboard
Every rank and its EXP