The type command for bash will tell you whether a command is a shell built-in or an executable on it`s own. This is very simple to use.
This example shows how it works.
[email protected]:~$ type -a echo echo is a shell builtin echo is /bin/echo
The type command itself is a shell built-in, that allows you to tell what a Linux command is. Use the whatis command to get information about a Linux command.
This example shows information about ls.
[email protected]:~$ whatis ls ls (1) - list directory contents
The info command is also very useful for reading info pages about various Linux commands.