To add an additional path temporarily (i.e., until you logout of the current shell) to the end or beginning of the current PATH respectively
To add an additional path permanently, add the same command to your .bashrc or .bash_profile or equivalent for the shell you use. This will add it only for the use who's profile you update (similar to config.sys for a single user). To add an additional path system-wide add the above to /etc/profile (similar to config.sys) or equivalent. I don't know how Ubuntu is configured.