You need to first extract file you've downloaded from ThemeForest, the theme is inside of this zip file along with documentation, license, psds and other files. You need to upload only theme folder to your WordPress.
This might be helpfull:
http://support.envato.com/index.php?/Knowledgebase/Article/View/269/0/my-wordpress-theme-isnt-working-what-should-i-do