Once purchased, you will be sent a link to download a zip file.
This assumes you are running PHP 5.5 or newer. (I suggest at least PHP 5.6)
You will need to extract this onto your web server somewhere so it can be accessed from the web.
You will also need to change the permissions so that the server has full write access to the storage and assay folders.
Note: This assumes that you have SSL set up on your server… If you don’t WHY NOT? And a guide to get SSL set up for free can be found here: https://certbot.eff.org/
You now want to work through the Common Setup