It has become a trend for top sites especially news and content aggregrators to show your site inside a frame (if you see a site toolbar on the top of the page it's usually using a frame).
Basically the visitor never leaves the site using the frame although they are viewing content created by you! This is done for multiple reasons and one is to improve the metrics of the site using the frame as 'visitor time on site' will improve only for the site using the frame and not you.
Purpose of No Frames plugin is to detect these cases and break your site free from the shackles of the frame, thus presenting the user with your full page.
This not only improves your visitor experience but your site metrics as well.
1. Upload the whole plugin folder to your /wp-content/plugins/ folder.
2. Go to the Plugins page and activate the plugin.
3. That's all, everything will work automatically
You can also visit my other WordPress Plugins.