How do I make a script where I pull out a Tool and it Increases my health?

Alright, so I wan't to pull out a Tool called Lightsaber, And upon pulling it out, It increases my health to 500.

Not sure what you mean, but do you mean this? Put this script inside the tool.

local Tool =script.Parent
local Char = Tool.Parent.Parent.Character
local value = 500
Tool.Equipped:connect(function(mouse)
Hum = Char:WaitForChild("Humanoid")
if Hum ~= nil and Hum.Health ~=0 then
		Hum.Health = Hum.Health + value
	end
end

Put this LocalScript into the Tool.

local plr = game.Players.LocalPlayer
local tool = script.Parent

tool.Equipped:connect(function()
	plr.Character.Humanoid.Health = plr.Character.Humanoid.Health + 500
end)