PrBoom is a modern doom game engine or "doom-port" to play id
Software's Doom, Doom II, Doom expansion packs and custom "iwads"
or mods (It doesn't include the game itself). It aims to be the most
stable Doom port with the highest compatibility to the major Doom
versions.

If you don't own any of the Doom games, get the shareware doom1.wad from
http://www.libsdl.org/projects/doom/data/doom1.wad.zip, unzip it, and
rename it to lowercase:  mv DOOM1.WAD doom1.wad
Then copy doom1.wad to /usr/share/games/doom/

If you have one or all of the main Doom data files from idSoftware -
either doom.wad, doom2.wad, tnt.wad, or plutonia.wad from one of the
commercial Doom games, copy them there too.

Highly recommended to play the Doom background music:
TiMidity++ with eawpats or freepats (all available at SlackBuilds.org)

Suggested: Take a look at the docs, man pages, or visit BahdKo at
http://www.doom2.net to learn how to watch demos, info, files, etc.
A great help for newcomers. (You may need a proxy to visit this url)