First urdf file

edit

I get the following errors and no model shows on the screen:

pci id for fd 24: 80ee:beef, driver (null)
libGL error: core dri or dri2 extension not found
libGL error: failed to load driver: vboxvideo

This error isn't really related to any problems with your URDF or your package: RViz is trying to initialise the OpenGL subsystem, but that apparently isn't working properly in your VirtualBox vm.

I'd make sure you can run 3D / OpenGL applications in your VM first, before continuing with ROS (or at least: if you want to run things like RViz / Gazebo, as those tools will require a working OpenGL pipeline).

Edit: also:

the tutorial says to roslaunch with display.launch but never says what that file contains

I'm guessing 'the tutorial' is Building a Visual Robot Model with URDF from Scratch on the wiki. If so, it doesn't tell you anything about display.launch because that is a file that you're supposed to re-use (so not re-create), by just launching it from the urdf_tutorial package, as the example command line shows you:

roslaunch urdf_tutorial display.launch model:=urdf/01-myfirst.urdf

Where urdf/01-myfirst.urdf is the path to your own urdf file. So in your case that would probably be (using the modified command explained a little later in the same tutorial):

roslaunch urdf_tutorial display.launch model:='$(find urdf_practice)/urdf/urdf_practice_file.urdf'

(but note that that would require urdf_practice to be on the ROS_PACKAGE_PATH (ie: you need to have (re)built your workspace after adding that package)).