Basic commands
Linux system administrator spends most of his time in terminal using commands to manage the system. So it is necessary to get familiar with basic commands to navigate in shell to control your system.
LPI Learning Material 101 - Topic 103.1 (Pages 169 - 191)
Unix shell
At its base, a shell is simply a macro processor that executes commands. The term macro processor means functionality where text and symbols are expanded to create larger expressions.
A Unix shell is both a command interpreter and a programming language. As a command interpreter, the shell provides the user interface to the rich set of GNU utilities. The programming language features allow these utilities to be combined.
Some of the well known and commonly used shells are i.e. sh, bash, zsh etc.
Documentation and help within shell
You might not know all commands or their syntax to run the command, but you have to be able to find your way out. Most of the command in shell has some type of help files which you can view within the shell and find more about usage of the command.
man is an interface to the system's reference manual.
man <command>
man ls #this will view manual pages for ls command
Also most of the command can show you basic usage by executing them with option --help or sometime it can be shortened to -h.
ls --help
docker -h