Install this theme normally after you already have Joomla installed and ready to go.
The best and the recommended way of installation is using the Quickstart package (which is a pre-installed, pre-configured Joomla with the milestone template). You can get started quickly if you use this package.
Quickstart is an exact copy of the template demo you have seen in your website. It has complete Joomla instance with the template installed. You just have to extract it and follow the installation wizard.
Installation of Quick start Package:
Extract the quick start zip pakage in your website root. This is either public_html or www in the hosted servers.
If you have installed XAMPP or MAMP or WAMP, you will have to extract this into the httpdocs folder
After the extraction, point your browser to url of the public root or the folder where you extracted. Example: Let us say, you have created a folder called milestone under the public_html folder (called your web root) . Then you extracted the zip inside the milestone folder.