Shell builtins work significantly faster than external programs, because there is no program loading overhead. However, their code is inherently present in the shell, and thus modifying or updating them requires modifications to the shell. Therefore shell builtins are usually used for simple, almost trivial, functions, such as text output.
Because of the nature of operating systems, some functions of the systems have to be implemented as shell builtins. The most notable example is the
cd command, which changes the working directory of the shell. Because each executable program runs in a separate process, and working directories are specific to each process, loading
cd as an external program would not affect the working directory of the shell that loaded it.
logoutfunction, which terminates the session. This function has different names depending on the shell.
Some examples from bash include
$ cd ..
Loops (if, while, for and such)
help bash-builtin command will list all builtins.
Command Bourne Almquist Sash