Linux traditionally operates in text mode. Linux encourages its users to acquire knowledge and to become independent. Inevetably, you will have to read a lot of documentation to achieve that goal. The more docs you read, the easier it will become and the faster you will leaf through manuals. Make reading documentation a habit as soon as possible. When you don't know the answer to a problem, refering to the documentation should become a second nature.
When programmers can read, distribute and change code, the code will mature. People can adapt it, fix it, debug it. This software will be more flexible and of a better quality than software that has been developed using the conventional channels, because more people have tested it in more different conditions than the closed software developer ever can.
When we run the command, the shell sees that it should execute that command, and
then searches through the :-separated list of directories in $PATH for a file by
that name. We can find out which file is executed for a given program name using the
which command. We can also bypass $PATH entirely by giving the path to
the file we want to execute.
r - list its contents of a directory
w - add/remove files in a directory
x - permission to enter a directory
Operations like |, >, and < are done by the shell, not by the individual program. They just read from their input and write to their output, whatever it may be.
Sources list: /etc/apt/sources.list
Console fonts: /usr/share/consolefonts/
To list essential packages in Debian:
dpkg-query -Wf '${Package; -40}${Essential}\n' | grep yes