Linux has a command for almost any tasks and most of them are intuitive and easily interpreted.
Getting Help in Linux
man <name> Read the manual page of <name>.
man <section> <name> Read the manual page of <name>, related to the given section.
man -k <editor> Output all the software whose man pages contain <editor> keyword.
man -K <keyword> Outputs all man pages containing <keyword> within them.
apropos <editor> Output all the applications whose one line description matches the word editor.When not able to recall the name of the application, use this command.
help In Bash shell, this will display the list of all available bash commands.
help <name> In Bash shell, this will display the info about the <name> bash command.
info <name> View all the information about <name>.
dpkg -l Output a list of all installed packages on a Debian-based system.
dpkg -L packageName Will list out the files installed and path details for a given package on Debian.
dpkg -l | grep -i <edit> Return all .deb installed packages with <edit> irrespective of cases.
less /var/lib/dpkg/available Return descriptions of all available packages.
whatis vim List a one-line description of vim.
<command-name> --help Display usage information about the <tool-name>. Sometimes command -h also works, but not for all commands.
User identification and who is who in Linux world
hostname Display hostname of the system.
hostname -f Displays Fully Qualified Domain Name (FQDN) of the system.
passwd Change password of current user.
whoami Username of the users logged in at the terminal.
who List of all the users currently logged in as a user.
w Display current system status, time, duration, list of users currently logged in on system and other
last Who recently used the system.
last root When was the last time root logged in as user.
lastb Shows all bad login attempts into the system.
chmod Changing permissions - read,write,execute of a file or directory.
Process related information
top List all processes sorted by their current system resource usage. Displays a continually updated display of processes (By default 3 seconds). Use q key to exit top.
ps List processes currently running on current shell session
ps -u root List all of the processes and commands root is running
ps aux List all the processes by all users on the current system