Getting back to this question, I managed to get the camera working, however it won't stay at the spot you drag it to. I've tried everything I can think of to keep the camera in the same place the player moves it to, but it keeps going back to its original location.
At first, I tried on_mouse_middle == 1 but all that happened was that the screen just moved a little when you click the middle mouse button. Then I did the While loop. You can drag the camera around; however, once you let go of the middle mouse button, the camera goes back to its original location rather than stay where the player puts it.
What do I need to do to get this working? it's been bugging me. Thanks in advance.