What are some useful computer related technical skills, not involving programming, I can learn within a day?

Piping.  It is one of the most powerful skills available that few people who don't spend a lot of *NIX command line time know. What is it:   Take one program:   Dir (or ls) and pipe the output to ANOTHER program (say findstr or grep) and then DO something with that. For Windows command line a completely trivial example you could probably do with just DIR itself or xcopy alone:   dir  |   findstr /b /i *.xlsx |  sort The above is so common that it is pretty much already included in dir, but the IDEA is the powerful tool worth learning. Note too:  learning to use tools like "FindStr" (Windows) or Grep (Linux but available for Windows) is a powerful thing to have at your disposal. Piping in PowerShell (Windows) is FAR richer than this idea of piping output TEXT, but a bit more complex to learn and appreciate. Piping things is frequently a way that I collect and filter data to prepare it for IMPORT into Excel where you can do all sorts of the things worth learning like the Pivot Tables mentioned above or CHARTING. -- HerbM

Setting up a torrent framework, a download manager, updating firefox with add-ons and learning the procedure to crack software.

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Setting up a basic, DNS/Bind server could be learned in one day. Assuming IPv4, only. You could probably learn the basics of the SAMBA smb.conf file in a day. A lot of *nix programs use plain text files for their configuration, so it is very possible to learn the basics of these programs very quickly.