First thing you need to ask yourself is, "Do I want the path to be affected for all users or just for this one user?"
If the answer is all users, then you can do one of two things:
1. Edit the /etc/profile file, which will contain the system path set command (just search for PATH=). Edit this line to add the new path, then save and exit. To cause the changes to take effect, simply run it, as:
(yes, that's a dot, a space, then the path of the file)
If you don't feel comfortable editing the /etc/profile file, then
2. Edit the file /etc/rc.d/rc.local, and add a new path adjust to the end of the file. If the file doesn't exist, simply create it with a text editor, and put your new path export statement in:
Those will both cause the changes to affect every user.
If you don't want it to affect every user, simply do like the others have suggested and simply create the file ~/.profile and edd the path statement to it. That do what you want!
Hope this helps!