make part rotate to cursor?

Eh, you need some CFrame witchcraft. But it's fairly simple to do!

One of the constructors of a CFrame is as follows:

CFrame.new ( Vector3 Position, Vector3 LookAt )

For example:

CFrame.new(Vector3.new(0, 10, 0), Vector3.new(5, 0, 0))

Will create a CFrame located at {0, 10, 0}, oriented towards {5, 0, 0}. And that's all! Now all that's left is to plug in what you know already:

-- Local script
local mouse = game.Players.LocalPlayer:GetMouse()
local part = workspace.Part

mouse.Move:Connect(function()
    part.CFrame = CFrame.new(part.Position,mouse.Hit.Position)
end)

Hope I helped!