Well, the parallel view you get is your computer on one side, and the server on the other. You can drag and drop files back and forth as you want that way, without needing to open additional windows. Why don't you try it a little more and see if you can get it to work. Don't worry about messing things up too much, as I have backups I can restore in the worst case. Don't get me wrong, it's not that I don't want to help you, but it really would be better if you can learn to do this on your own, then maybe you'll be more prone to make updates, even for more minor things.
As for the current "brokenness" of the page... It looks like you simply uploaded "webpage.html" to the wrong folder. It needs to go inside the "public_html" folder, along with the rest of your site. You put it one folder above that. You should be able to just drag the file into "public_html" and fix things.