What are the properties of a leaderboard?

If you aren't already, you could use ROBLOX Studio to view the properties. Other than that, I don't know what you mean by leaderboard. Please elaborate.

As for the example code. This should be a normal ROBLOX leaderboard.

game.Players.PlayerAdded:connect(function(p)
	l=Instance.new("IntValue",p)
	l.Name="leaderstats"
	t=Instance.new("IntValue",l)
	t.Name="Time"
end)

After that you can edit values by saying:

game.Players.PlayerAdded:connect(function(p)
	l=Instance.new("IntValue",p)
	l.Name="leaderstats"
	t=Instance.new("IntValue",l)
	t.Name="Time"
end)

while wait(1) do
	t.Value=t.Value+1
end

Hope it helps.