Linux

The commands man and apropos are your friends to get you started.

Learning how to use specific tools like grep, sed and awk is a case of getting started by using them. Most of the subsequent learning process will focus around how to create regular expressions (regex), for which there's also a manpage.

The "typical example" for a dd command is like saying, "here's a great way to shoot yourself in the foot". A better way is to understand that most of these tools follow the UNIX philosophy:

1. Make each program do one thing well. To do a new job, build afresh rather than complicate old programs by adding new "features".
2. Expect the output of every program to become the input to another, as yet unknown, program. Don't clutter output with extraneous information. Avoid stringently columnar or binary input formats. Don't insist on interactive input.
3. Design and build software, even operating systems, to be tried early, ideally within weeks. Don't hesitate to throw away the clumsy parts and rebuild them.
4. Use tools in preference to unskilled help to lighten a programming task, even if you have to detour to build the tools and expect to throw some of them out after you've finished using them.

Once you "grok" that, you'll be in a much better place.