Basic Webdesign Account Storage Files

I am trying to create a website that allows users to create an account. I would like to be able to (as an admin) upload a media file, automatically process it (perform fairly resource intensive processes), and distribute unique variations of that file to each user account.

I am fairly new to web and database design so I was hoping for a little direction. I registered a domain name using NameCheap.com and am using Bluehost.com webhosting to host the website.

I am not really sure where the "process it" step should take place or how to link media to a user account. I would assume I set up some sort of relational database through mysql to link user account emails, passwords, etc. But how do I link and store media files to an account? Is there a name for this type of service? Would this service be able to execute my server-side code to modify my media files?

I apologize if this is in the wrong section and/or a very basic question as this is my first post.

Thanks for any help.