Once you have downloaded the zip file from Themeforest, unzip it using your standard zip software.
When it has finished you should have a folder with the following files & directories inside.
|backgrounds/||36 bundled backgrounds & retina versions|
|demo/||Demo content data for import|
|documentation/||contains a link to these docs|
|licensing/||theme licence files|
|psds/||all the themes layered PSD files for Adobe Photoshop|
|smartbox-theme-ver.zip||the wordpress theme zip file ( for installation into WordPress )|