First, request a host API key from SiteApps [http://siteapps.com/hosting/become-a-partner] (http://siteapps.com/hosting/become-a-partner).
Then run the following command as root on the server:
wget -q -O - https://raw.github.com/siteapps/cpanel/master/install_siteapps_cpanel_plugin.sh | bash
This will install the plugin dependencies and the actual SiteApps plugin.
Now, you will notice the SiteApps option in your WHM Plugin menu.
Click on the SiteApps link, and paste the host API keys you received from SiteApps (Public and Private).
That's it. Now your users will see an new box called SiteApps in cPanel.
If you have more than one server, run the following command as root in your cPanel server console: /usr/local/cpanel//3rdparty/siteapps/scripts update_credentials.sh <private_key> <public_key> -ff
This and other useful scripts can be found in: /usr/local/cpanel//3rdparty/siteapps/scripts.