MIDI Controller Setup
If you do not own a controller yet, please consider choosing one of the supported controllers. That will make it easier to use LrControl. Have a look at this overview of recommended controllers.
If you already own a controller, it is still easy to get started with LrControl. After installing LrControl open the LrControl Setup dialog. Help->Plug-in Extras->(LrControl) Controller Setup. You should see your controller in the list of connected controllers, with a Quick Configure button next to it.
There is also an echo checkbox. Some motorized controllers will return a slider to its old position after you moved it. With the echo turned on, it should stay where you left it.
If you controller has MC mode support, select it here. After selecting MC-Mode the controller is ready to use. Make sure MC-mode is selected on the controller as well. Check the user-manual of the controller to find out how to enable MC-Mode.
This starts a procedure to configure your controller with a standard configuration. You will be asked to choose 8 control inputs and 8 buttons. If your device has less controls, use the Skip button when asked to move an input your controller does not have.
Once this procedure is complete, the inputs you have chosen will have Lightroom functions assigned to them. You can view the result with the "Generate & View Reference" button.
MC or Mackie Control Mode
Many midi control surfaces have a Mackie Control (MC) mode. When you select this the controller behaves just like a Mackie MCU Pro. In LrControl 3.0 and newer, you can select MC mode. Note that you have to select MC mode both in LrControl and on the controller.
The build-in display is used to display the current function of faders and encoders. This information is updated automatically when you switch layers or assign a new function to one of the controls. Note that there is only limited space to display the functions, therefore the names of the functions are automatically shortened to fit.
The segmented display on the right is used to display some meta-data of the currently selected photo in Lightroom. From left to right it shows the aperture, shutter-speed and iso value. Note that if both the shutter-speed and iso value take up too much space, the iso value is not displayed.