I'm a newbie to this part of computing too, but I'm a veteran at most other things digital.
First, you should get the FileZilla FTP application (but other freeware apps are OK too--FileZilla is a bit simpler than most I've found).
Next, you gotta get your FTP site address stuff from your host, "Hostgator" or whatever. You type that into the address section in FileZilla: Open "File" upper L corner--select "Site manager"; go to bottom L of screen; add a new site; fill in your data you got from your host. You'll need to fill in your username and PW from your host. SAVE it all; then connect.
On the L sideof the screen in FileZilla are your local computer's hard drive files; you should find your theme files there before connecting to your host FTP site to minimize connect time. I do this only for security reasons, and to avoid "mouse click" blunders while in transfer mode.
After connecting to your host's FTP:
On the R side of the screen you find your folder online where you want to send your stuff. You just L click/hold mouse on your local files and drag them to your remote folder; in other words, you go from L to R side of screen, and drop them.
Of course, you'll run in to some other problems along the way, but that's part of the fun and learning ;))
Hope this helps