Just so you know, sharing these kind of details (internals working of Steam developer stuff) is against NDA AFAIK, which is why it's hard to find information on it.
My recommendation is to read:
https://help.yoyogames.com/hc/en-us...bling-Steam-Integration-In-Your-Desktop-Games
Then read the Steamworks documentation. It explains a lot of the finer details for each section. Finally, join the Steamworks discussion group and search that for answers, posting questions if you can't find an answer relevant to what you are asking.