Hi,

This is a common issue with WordPress themes. You first need to unpack the package you got from themeforest. Inside the package is the actual theme zip 😉

Envato also has a nice article about it: http://support.envato.com/index.php?/Knowledgebase/Article/View/269/0/my-wordpress-theme-isnt-working-what-should-i-do

Cheers!