Installing a New Add-on
The exact procedure for installing a new add-on will be directed by the creator of that add-on. However, in general, the procedure will be as follows:
Download the add-on and unzip it.
Upload the add-ons files into your XenForo installation. This will usually create a new directory within the library/ directory in your XenForo installation. In general, this shouldn’t overwrite any existing files.
From your control panel, go to the "install add-on" page. The add-on will have provided an XML file somewhere within it. Upload that file here and submit the form.
So here we go, firstly, Extract your Zip file if you haven't done that already. Then connect to your site via FTP. In the Add-on files that you just extracted, open the "upload" folder to reveal the folders inside of it (usually something like Library and JS or whatever. Simply upload these folders into your forum directory... ie... if your forum is located at www.yoursite.com/forum then upload them into the /forum directory. If it's www.yoursite.com/community then upload them to the /community directory.
Once you uploaded them, open up your forum and go to your ACP (Admin Control Panel) and go to "List Add-ons". At the top right click "Install Add-on" and choose the XML file that your Add-on came with.
If you need further help, I can literally show you how to do it.