How do you add sounds when you get over a TextButton?

Well, you can use MouseEnter function provided by Roblox. It will detect whether the mouse has entered the TextButton. Also, you can use MouseLeave to detect if the mouse left the TextButton.

A sample code:

-- Local Script inside the TestButton

local TextButton = script.Parent

local function Enter() -- Creating a local function
	local sound = Instance.new("Sound") -- Creates a sound object
	sound.Parent = TextButton
	sound.Name = "TestSubject"
	sound.SoundId = "rbxassetid://12345678" -- An example

	sound:Play()
end

local function Leave()
	local Sound = TextButton:FindFirstChild("TestSubject")
	
	if Sound then -- If the Sound object is found
		Sound:Stop() -- Stops the sound
	end
end

TextButton.MouseEnter:Connect(Enter)
TextButton.MouseLeave:Connect(Leave)

Lemme know if it helps!