Manual/Help

Man

Opens the manual for a given command in less. This only works on external commands, aka ones not in bash.

man ls

Opens the manual for a given bash command.

man history

Shows you where external commands are stored.

which ls

Tells you weather the command is external or a bash command

type echo

-a - shows you all the implementations of that command (yes this is actually very important)

Auto completes commands, passing no argument shows all the built in commands

compgen

-b -

Term	Definition
External command	A command that is not built into bash. External commands will exist in the bin folder
Built-in	A command that is built into bash

Commands can be both an external command and a bash command. Echo is a good example, so just be wary which one you are using.