How do I make this tool select the part that the player clicked on?

Hello, I'm making btools. I'm wondering how do you get the part that the player clicked on? I want it so that when you click on the part, a decal appears on the part you clicked.

local tool = script.Parent

local function Texture2D(point)
    local Texture2D = Instance.new("Decal")
    Texture2D.Texture = "rbxassetid://6423847544"
    Texture2D.Face = "Top"
    Texture2D.Parent = point
end

local function onActivated()
    local human = tool.Parent.Humanoid
    Texture2D(human.TargetPoint) 
end

tool.Activated:Connect(onActivated)

Update: @FirezDevv supplied me a script, but it doesn't work and he just suddenly left when I reported an error. Can anybody help? It's a server script is parented to a tool, and the error I get is "Workspace.UnityEngine.Texture2D.Script:15: attempt to index nil with 'GetMouse'".

local tool = script.Parent

local function Texture2D(point)
    local Texture2D = Instance.new("Decal")
    Texture2D.Texture = "rbxassetid://6423847544"
    Texture2D.Face = "Top"
    Texture2D.Parent = point
end

local function onActivated(mouseT)
    local human = tool.Parent.Humanoid
    Texture2D(mouseT) 
end

game.Players:FindFirstChild(tool.Parent.Name):GetMouse().MouseButton1Down:Connect(function()
onActivated(game.Players:FindFirstChild(tool.Parent.Name):GetMouse().Target)
end)