How Do I make my Advanced FireBall Do Damage?

function onKeyDown(key) 
key = key:lower() 
if key == "z" then 
script.Disabled = true 
Player.Character.Humanoid.WalkSpeed = 10 game:GetService("Chat"):Chat(Player.Character.Head,"Fire Style:Fire Ball Jutsu!!")
 x = Instance.new("Part") 
x.Shape = "Ball"
 x.BrickColor = BrickColor.new("Maroon") 
x.Size = Vector3.new (10, 10, 10) 
x.CanCollide = false
 x.TopSurface = "Smooth" 
x.BottomSurface = "Smooth"
 x.Name = Player.Name

x.Transparency = 0.6 y = Instance.new("BodyVelocity")
 y.maxForce = Vector3.new(math.huge, math.huge, math.huge)
 y.velocity = Player.Character.Torso.CFrame.lookVector*55
 x.Parent = workspace 
y.Parent = x 
x.CFrame = Player.Character.Torso.CFrameCFrame.new(0,0,-10) Player.Character.Humanoid.WalkSpeed = 16

game.Debris:AddItem(x, 1.5)

wait(4)
 script.Disabled = false
 end
 end
 mouse.KeyDown:connect(onKeyDown)