What information should I look up to set up a database between a website and a game?

I'm developing a game in UE4 that will be connected to a website for supplemental purposes, so I need both platforms to be able to login using the same information. Rather than get you all to hold my hand, what topics should I research to learn what I need to do to get this up and running? I know that a database will be involved, but I have no idea how to use a database or how hook it up between different platforms.

Thanks in advance!