How do I make a moving GUI when clicked?

If you want it to move to a certain position when clicked you can do

--Must be in a TextButton or ImageButton
script.Parent.MouseButton1Down:connect(function()
    script.Parent:TweenPosition(UDim2.new(.5, 0, .5, 0));
end);

This will move the gui to the position (.5, 0, .5, 0) on screen. The first set (.5, 0) is the X position, in this set we have percent of screen (.5) and pixels (0) the second set is the same but with Y position. You can change these numbers to be whatever you want.