Mouse locks when you click on the game window, press ESCAPE or TAB to unlock the mouse.
To multiselect click and drag with Middle Mouse or Q. Fill the nodes with B or delete them with N. Middle Scroll or X+C to change texture. V to paste selected nodes to pointed position.
Arrow Keys can be used to move the view around.
Your state is automatically saved on exit.
You can customize the 17 block tileset, in your dataPath you will find a tiles.ppm image file, edit this file and save it as a PPM with a P6 272 16 255 header. Krita or KolourPaint can edit PPM files.
Sensitivity as the 1st command line parameter default is 0.003 `./voxelpaintpro 0.003`.