You can either use the automatic plugin installer or your FTP program to upload it to your wp-content/plugins directory the top-level folder. Don't just upload all the php files and put them in /wp-content/plugins/.
Activate the plugin through the 'Plugins' menu in WordPress
Visit your Simpletabs menu
Create tab post
Add Short Code [Simpletabs] To Any WordPress page
Add a post thumb to a desired post.
Compatible up to: 3.4.2 Last Updated: 2012-9-7 Downloads: 2,899