Installation of this plugin is exactly the same as any other wordpress plugin. If you 
are uplading via your wordpress admin panel, simply upload the ngg-pup.rar file
through the client and wordpress will automatically unpack the file. Once wordpress
is done, you are given the option of activating it. Simply press activate, and voila
you are done. 

If you are uploading the file manually, unpack the ngg-pup.rar file. This will create
a folder called Ngg_pup. Take this folder, and manually it via FTP or whatever method
you prefer, and store it in your plugins folder which are typically stored in 
your-website/wp-content/plugins. Once uploaded, you should see:
your-website/wp-content/plugins/Ngg_pup. 

Once the plugin is manually uploaded, go into your plugin manager page in wordpres
and manually activate the plugin by clicking on the activate link. 

It's recommended that after activation, you go to the settings page and 
configure the plugin to what you want.