Can anyone help me change this script so i hit F and it fires and not click my mouse?

this script here

local Selected = false 
local Shoot = true 
function Click(Target) 
if(Target.Target.Parent:findFirstChild("Humanoid")~=nil)then 
Target.Target.Parent.Humanoid.Health = 0 
end 
local P = Instance.new("Part") 
P.Name = "Laser" 
local Place0 = script.Parent.Parent.Parent.Character["Left Arm"].CFrame 
P.formFactor = 0 
P.Size = Vector3.new(7,7,(Place0.p - Target.Hit.p).magnitude) 
P.CFrame = CFrame.new((Place0.p + Target.Hit.p)/2,Place0.p) 
P.Parent = game.Workspace 
P.Material = "Neon"
P.Color = Color3.new(106) 
P.Transparency = 0 
P.Reflectance = 0.5 
P.Anchored = true 
P.CanCollide = false 
local E = Instance.new("Explosion") 
E.Position = Target.Hit.p 
E.Parent = game.Workspace 
for i = 1,10 do 
P.Transparency = 0.5+(i*0.05) 
P.Reflectance = i*0.05 
wait(0.1) 
end 
P:Remove() 
end 
function Select(Mouse) 
local Arm = script.Parent.Parent.Parent.Character:findFirstChild("Left Arm") 
if(Arm==nil)then 
script.Parent:Remove() 
script:Remove() 
end 
Selected = true 
local Torso = script.Parent.Parent.Parent.Character:findFirstChild("Torso") 
if(Torso==nil)then 
script.Parent:Remove() 
script:Remove() 
end 
local ArmWeld = Torso:findFirstChild("Left Shoulder") 
if(ArmWeld~=nil)then 
ArmWeld.Parent = nil 
end 
--Mouse.Button1Down:connect(function()Click(Mouse)end) 
function onKeyDown(key)

if key == "t" then
Arm.Anchored = true 
while Selected do 
local Place0 = script.Parent.Parent.Parent.Character.Torso.CFrame 
Place0 = Place0 + ((Place0 * CFrame.fromEulerAnglesXYZ(math.pi/2,0,0)).lookVector * 0.5) + (Place0 *        CFrame.fromEulerAnglesXYZ(0,math.pi/2,0)).lookVector 
local Place1 = Place0 + ((Place0.p-Mouse.Hit.p).unit * -2) 
Arm.CFrame = CFrame.new((Place0.p + Place1.p)/2,Place0.p) * CFrame.fromEulerAnglesXYZ(-math.pi/2,0,0) 
wait() 
end 

end
Arm.Anchored = false 
if(ArmWeld~=nil)then 
ArmWeld.Parent = Torso 
end 
end 
function Deselect() 
Selected = false 
end 
script.Parent.Selected:connect(Select) 

I tried to were inset of a mouse click...you hit F and it would fire, I have no clue what to do.. help?

I'm not really going to go into too much detail because this isn't even your code, but I'll post a link to a useful wiki page if you really want to learn how to do this. Here is the code you would use to fire something when the F key is pressed:

game:GetService("UserInputService").InputBegan:Connect(function(input, gpe) --when any input from the player is detected
	if gpe then return end --if the player is chatting then do not run the code
	if input.KeyCode == Enum.KeyCode.F then --if the input detected is the "f" key being pressed
		--code
	end
end)

Here are some useful links:

https://wiki.roblox.com/index.php?title=API:Class/UserInputService https://wiki.roblox.com/index.php?title=API:Class/UserInputService/InputBegan