Panning the wheel in the mixer adjusts the pan for the track.
You can have track automation and object automation.
For track automation, right-click in an empty area of a track and select Display Curves, Panorama, or in the Track Header, click on the popdown button beside Fx and turn on Panorama (or Volume, etc.). Now you can use the mouse to add points to the white line and moving the points up and down. Hovering over a point will show you the L&R values. If you subsequently move the wheel in the Mixer, it will put everything to the same level, so be careful.
Unfortunately, MMM Mixer does not allow automation during playback by moving the faders/wheels like in Movie Edit Pro or some other programs.
For object automation on an audio object, not MIDI object, right-click, Automation, Display panorama curve. You can now click on the line to add and move points. Or change the mouse mode (big arrow button at top right) to automation and you can draw in your curve. Also, right-click, Automation, Automation for this object, will open a dialogue box with more features that you can play with.