Feel a little embarrassed to ask, but my brain is killing me

and is asking me to go public for assistance.
How do I go about making a file for an External CSS? Thus far I have not faced a need for one and have just been playing around with having it Internal. Now IE6 is making my page look horrid and need I need to design the page(s) around it.
Do I go under the Public_HTML folder?
If so, do I create a new File and choose TEXT Document or HTML Document?
Or am I even on the right path?
Any input would be highly appreciated.
