how do i run a function when a character is added to the world?

i need to define the players character as a variable and i need to wait until its added its giving me index nil "CharacterAdded" for the line that should run the code

local function GetDistance(p1,p2)
    local Distance = (p1.Position - p2.Position).magnitude
    return Distance
end
players = game:GetService("Players")
local function start()
    local character = players.LocalPlayer.Character.PrimaryPart
    local button = script.Parent
    while wait(0.1) do 
        if GetDistance(button - character) > 10 then
            print("E")
        end
    end
end


game.Players.PlayerAdded:Connect(function() 
    game.Players.LocalPlayer.CharacterAdded:Connect(start)
end)