How can I get this script to work (Basic Level: Properties and Functions)?

The function is never called because the script is stuck on the while loop, code is read from up to down, it never reads the calling part because its looping over and over again in the while loop, to fix this put the part where your calling the function before the loop

function light()
    local nl = Instance.new("PointLight", workspace)
    nl.Parent = script.Parent
    nl.Color = script.Parent.Color
    nl.Brightness = 2
end

light()

while true do
    wait(1)
    num = math.random(1,2)
    if num == 1 then
        script.Parent.Color = Color3.new(255, 0, 0)
    elseif num == 2 then
        script.Parent.Color = Color3.new(248, 248, 248)
    end
end

function light()
    local nl = Instance.new("PointLight") -- I removed the workspace modifier. Try not to use this when creating instances. Causes lag.
    nl.Parent = script.Parent -- this is the proper way to parent an instance.
    nl.Color = script.Parent.Color
    nl.Parent.Changed:connect(function(stat) -- added a function in the light to update its color 
    if stat == "BrickColor" or stat == "Color" then -- make sure the color was what changed
    nl.Color = nl.Parent.Cololr
end
end)

    nl.Brightness = 2
end

light()

while true do
    wait(1)
    num = math.random(1,2)
    if num == 1 then
        script.Parent.Color = Color3.new(255, 0, 0)
    elseif num == 2 then
        script.Parent.Color = Color3.new(248, 248, 248)
    end
end