If you want to make systemwide changes to your path, you have to do it in /etc/profile.
But it is better to adjust the path settings in the users home directoy by editing the ".bash_profile" (if you are using the bash).
Add new path to the line "PATH=$PATH:$HOME/.....:/
After editing this file you have to "source" it with the following command: ". ./.bash_profile". By doing so, the .bash_profile is beeing re-read by the shell.
For documentation take a look at http://www.linuxdoc.org.
There you will find most of the stuff you need.