Blake - the easiest commandline editor to use on OS X is pico, the keyboard commands a all listed along the bottom of the screen, so you can't get lost.

So, you would start editing the file with:
pico ~/.bash_profile

You'd add in the line from the instructions, hit ctrl+x to exit, it will ask if you want to save, say yes. Then, for the changes to take effect, close the Terminal and open a fresh one.

Hope that helps,

Bart.