By pressing R (with a puzzle loaded), you access the scatter settings window that will allow configuring how the program will scatter the pieces on the board. It will also allow undoing the last scattering operations.
Scattering can be useful when you are stuck not finding more pieces, to make room in some zone of the board, etc. Optionally the program can scatter the pieces sorting them approximately by color to make easier the selection of pieces. There's an option Scatter grouping by color for this, check it and the program will sort the pieces by color. (The option will stay active/inactive the the next times it scatters the pieces)
Scattering can be done quickly by pressing the keys Ctrl+R or Alt+R . In the Scatter Settings window configure what will do each of these keyboard shortcuts. Click on the top of the window which key you want to configure.
Next go the different options to choose what pieces not to move and
also to control on what zones in the board will not be placed pieces.
Check the options you wish and press OK to save the settings. From now on when you press the corresponding keyboard shortcut the program will perform the scattering per these settings.
The window has also a button labeled Scatter , this one allow performing the scattering from that window and eventually undoing the movements.
Undo will undo the last scattering even if you did it with the keyboard without this window open, so if you scatter unintentionally you can press R and then the button Undo to have the pieces placed as they were before.
Note: Additionally to scattering with Ctrl+R and Alt+R , you can first draw a "selection rectangle" and right click into it to have a menu with additional options that take the rectangle into account. Related: Handling multiple pieces