It's really pretty simple, you can either run rawproc like you would any other program from the Start menu, or double click the desktop icon.
You can make rawproc a lot easier to get to if you either specify it as the default program for the image types you want to work with, or getting it into the list of programs you get when you right-click on a file and select "Run With" from the popup menu. Both Windows File Explorer and Nautilus in Ubuntu have a "Run With" menu entry that allows this.
If you put the rawproc install directory in your PATH environment variable, you can run rawproc from the command line:
rawproc DSC_0001.NEFwill run rawproc and open the image file specified.
The -s switch is a unique rawproc feature. If you've previously created an image with rawproc, it'll save the command sequence used to create it in the image's EXIF. Using -s to open the image will actually open the image you started with (if it finds it in the same directory), and apply the tools in sequence to reproduce the image you intended to open:
rawproc -s DSC_0001.jpgIf DSC_0001.jpg was created by rawproc from DSC_0001.NEF, this command will open the .NEF file and apply the tools in sequence to recreate DSC_0001.jpg.
The -c switch lets you specify a configuration file. This lets you set up one configuration for your camera's raw images, and another for editing others' raw files (think, PlayRaw...)
rawproc will also open an image when it is dragged from a file explorer to any where in the rawproc window. rawproc also support opening images that are dragged to a desktop icon, but in Ubuntu 18.04 and greater, this doesn't seem to work anymore... :(