A Newbie Question: How Can I Upload a Template CSS Code?

I would like to upload an Archive template stylesheet to my Website.

– I have created a Child Theme directory through my host, GoDaddy.
– I have a CSS stylesheet code ready.
– I have tried to upload through GoDaddy’s FTP File Manager, but no luck — got an error message “Missing Plugin.”

Here is my Archive page: http://olivetjournal.com/2013/06
Here is my other question page for the background: http://wordpress.org/support/topic/how-to-change-archive-page-template?replies=15

Just need to know where I can go to upload it, and how to do it.

Thanks!