Difficulties adding new themes/editing themes

How do I add new themes? I seem to be experiencing some diffulties. First what I did was downloaded the file and saved it to my computer, but it will not let me open it because it is a WinZip file which I do not have paid for. Once i uploaded it into the wp-content/themes directory it showed up on the main page as a “Broken file”.

Also, how do I edit the theme editor. Is it aloud or no? If so please let me know how this is possible.