Der Schwarze Nebel is a mod for Valve's Half-Life 2: Episode Two, that presents a mix of Cinematic Mod and beta related content of Half-Life 2.
The tutorial shows how to use 7-Zip archiver to install the mod. The downloaded archive is split into "blocks" with extensions such as ".001" ".002" ".003" and so on. Depends on how many blocks you got. Note, that you must have all blocks downloaded and use the most recent version of 7-Zip. Otherwise the extraction process will be corrupted. Also, don't even try to use WinRar to extract the files here.