Plugin downloads are usually a .zip file containing a folder. You should unzip the file and move the folder to your qa-plugin directory.
For example if a plugin is called "myplugin" you should end up with the folder YourSite/qa-plugin/myplugin with failes inside such as qa-plugin.php (i.e. at YourSite/qa-plugin/myplugin/qa-plugin.php)