How do I start BRL-CAD?
BRL-CAD is a suite of more that 400 tools and utilities. The suite of applications are intentionally designed to perform a succinct task so that they can be chained together, scripted, and expanded upon in order to provide powerful flexibility.
That said, most users will be interested in using mged for editing geometry as a first step in getting started with BRL-CAD. Documentation on mged can be found in the share directory where BRL-CAD was installed. There is also extensive mged documentation available on the website under Documentation.
If you're on Windows, there should be an icon for MGED in your start menu or on your desktop. For any other platform, you should be able to run this in an X11 terminal: /usr/brlcad/bin/mged
How do I get a hard copy of what I'm looking at in MGED?
The File->Raytrace and File->Render_View->RT_Script menu options in MGED will generate a raster image of MGED's current view. The pix-png utility can be used to convert from BRL-CAD's .pix raw image file format to the .png file format, and can then be printed or embedded into other documents using other tools.
Additionally, the other File->Render_View options for generating standard Plot and PostScript output files of the MGED wireframe suitable for printing. The pl-fb and fb-png tools can be used to rasterize a Plot file to the .png format.
Finally, there are a variety of renderers and lighting models available in BRL-CAD that are useful for various purposes. The rt tool is the primary ray-tracer that is used for shaded view rendering. The rtedge and rthide commands are used for hidden-line renderings similar to what you'd want for generating drafting documents. rtwizard is a graphical 'wizard' tool that can be used to generate a variety of hybrid renderings.