How should I fix the laser damage from my code?

Hi guys, I'm doing my first game, basically it's a survival game, where you have machines that want to kill you, and you have to find a safe place. These machines are the loose lasers, two in each arm. The laser script has a problem, they were meant to deal damage, but they're not. They are lasers that are released in different directions. Here is the original script:

gun = script.Parent

function findNearestTorso(pos)
    local list = game.Workspace:children()
    local torso = nil
    local dist = 450
    local temp = nil
    local human = nil
    local temp2 = nil
    for x = 1, #list do
        temp2 = list[x]
        if (temp2.className == "Model") and (temp2 ~= script.Parent) then
            temp = temp2:findFirstChild("Torso")
            human = temp2:findFirstChild("Humanoid")
            if (temp ~= nil) and (human ~= nil) and (human.Health > 0) then
                if (temp.Position - pos).magnitude < dist then
                    torso = temp
                    dist = (temp.Position - pos).magnitude
                end
            end
        end
    end
    return torso
end

while true do
    wait(.5)
    local target = findNearestTorso(script.Parent.Position)
    if target ~= nil then
        local P = Instance.new("Part") 
        P.Name = "Laser" 
        P.formFactor = 0 
        P.Size = Vector3.new(10,10,10) 
                connection = script.Parent.Touched:connect(onTouch)
                local Distance = (target.Position - gun.Position).magnitude
        script.Parent.Mesh.Scale = Vector3.new(0.25, 0.25, Distance)
        P.CFrame = CFrame.new(gun.Position, target.Position)*CFrame.new(0, 0, -Distance/2)
        script.Parent.Mesh:Clone().Parent = P
                P.Parent = game.Workspace 
                P.BrickColor = BrickColor.new("Toothpaste")
        P.Transparency = 0
        P.Reflectance = 0
        P.Material = "Neon"
        P.Anchored = true
        P.CanCollide = true
        target.Parent.Humanoid.Health = target.Parent.Humanoid.Health - 100
        wait(1)
        P:remove()
    end
end

Well the idea is that the laser HAVE TO HURT IN THE TIME YOU GET ON, but I still do not know anything about roblox lua, so I'm in need of help. The idea is to deal damage when it hits, But when I hit no harm, I hope you guys help me.