Where to start- custom sidebar per post

Hi Guys,
I have a background in PHP development and this is my first look at customising wordpress more than basic settings and plugin installs.

What I want to do, is have a sidebar that appears for every post, however this content would need to be different for each individual post. For example, a youtube video about the post or contact form with details relating to the post.

Ideally, I’d like to edit the content when i click “edit post”

I am a developer, happy to get my hands dirty and code something, but where to start?
What is the terminology I need to look into in the docs etc to get me up to speed?
How would i achieve this, is it by creating new theme files, editing the child themes functions or creating a widget or add on?

Any advice or pointers in the right direction most appreciated thanks!