I can't guarantee it will work on your server setup, and I can't provide any support in making it work.
But the premise is simple:
1) You can install an add-on just by browsing your computer for the ZIP file you downloaded from the Resource Manager
2) You can install an add-on by providing your XenForo username and password and the Resource Manager URL for the add-on
Installing add ons with xenforo is pretty easy. Unzip the add on package and then upload the add on folder inside your library folder maintaining the structure intact and then install their .xml file through Install Add on section in your Acp. Also most ad dons come with a read me file. You can check that out too and if you run into difficulties with a particular add on, you can post at its support thread for help.