[How to create a media library]

I want to create a media library in the CMS, similar to how it is in WordPress but custom-coded in PHP on my own site.

Can this be done simply with a database connection or will the images need to be uploaded to a server?

Bit confused as to how it works and which is the best way to go about it.

Thanks for any help.

[Getting 'Fatal error: Uncaught Error: Class 'MySQLi' not found in']

I closed everything down last night and it was all fine, website was working as normal etc, but I've turned on the Xxamp server today and I am getting this error. Seems very random as nothing has changed since it was last on? 

Does anyone know how to sort this out and why I'm now getting this error? Thanks!

[How to get a checkbox to update a database onclick without a submit button?]

Which languages do I need to make this happen? And I am unsure of how to incorporate PHP within a javascript query and what jQuery functions I will need.