FPS Level up System?

How do I make a FPS level system? Where a certain amount of kills promotes you. Also. If you can't answer this, is there a wiki article?

If what you want is to calculate how many kills you need to get promoted this could be useful:

function CalculateKillsToPromote(Level)
	return Level*6
end

print(CalculateKillsToPromote(1) .. " kills needed to get a promotion")

Would that be placed in a leaderboard