How do I make a walk speed giving button?

You'd need to use a LocalScript inside of a TextButton inside of a ScreenGui. Insert the following code in it:

local player = game:GetService("Players").LocalPlayer

script.Parent.MouseButton1Click:Connect(function()
	local character = player.Character or player.CharacterAdded:Wait()
	local humanoid = character.Humanoid

	humanoid.WalkSpeed = 50 -- Change 50 to the WalkSpeed you want.
end)

The MouseButton1Click event fires when a player presses the button. Then the character variable waits for the character to load. Then finally, it changes the WalkSpeed of the humanoid. Also, this is not a request site, thank you.