How do I define mousebutton1down in this script????

The script:

local Players = game:GetService("Players")
local tool = game.Workspace.tool
tool.Equipped(function()
	mousebutton1down(function()
		local Money = Players.leaderstats.TIX
		local Money = Players.leaderstats.TIX
        Money.Value += 1
	end)
end)

I don't think you would need you would need to use an Equipped event, but you should probably use Activated event instead of MouseButton1Down, Activated means when you click with the tool equipped. So basiclly.

local Players = game:GetService("Players")
local Tool = game.Workspace.Tool

Tool.Activated:Connect(function()
	--Code Goes here
end)