Just need to read the instructions inside the readme.txt
== Installation ==
The installation process is very simple, extract the files. Copy the 'help-desk.php' and 'help-desk' directory into '/wp-content/wp-plugins/'
Note: not the plugins folder.
That’s it, the plugin is now activated.
wp-plugins doesn’t exist, he means mu-plugin, and voilà, it works!
See ya!