There might be a couple of tutorials that will help you to understand the difference between the operations like cutting, engraving and scoring, and the different way you need to create each kind of input.
You mentioned Inkscape, so since that is the program you are using, you can start with this:
PSD, which is a Photoshop format, creates bitmap style (raster) images and those can only be engraved with a laser. If you want to create cut lines, you will need to create vector paths, and for that you need a vector drawing program like Inkscape or Illustrator.
There is a list of suggested reading here, that will go a long way towards explaining the differences between vectors and rasters, and how they work with the laser.
The Glowforge team recommends first working through a few prints by following along with the examples shown here to learn where everything is:
That particular page is also handy if you have any problems to Troubleshoot and you can access it by clicking on the Support button in the app.
Once you have run through the sample prints, some of the customers have put together some handy Tips sheets and a lot of tutorials in the Tips and Tricks section of the forum.
Some good ones to start with:
Most are only a page or two, so just glance through them and remember to have fun!
