Add a directory to your $PATH
PATH is an environmental variable in Linux and other Unix-like operating systems that tells the shell which directories to search for executable files (i.e., ready-to-run programs) in response to commands issued by a user.
To do this you edit the .bashrc file in your home directory and append the following line (chaining the existing path additions) :
export PATH=/path/to/dir:$PATH
For example, to add the directory /usr/sbin, the following would be used:
PATH="/usr/sbin:$PATH"
You will need to source your .bashrc or logout/login (or restart the terminal) for the changes to take effect.
Sourcing executes the file that it was given as a parameter.
To source your .bashrc, simply type
$ source ~/.bashrc
witch is basically
. ~/.bashrc