Creating and Connecting RDMBS for a website

I'm currently a sophomore studying computer science and I am working on a project which required me to create a website/web app. I have done all of the HTML/CSS work and the last thing I need to do is create a RDBMS data server, and display the results on a table in some of the pages.

I was able to create a .db file with all the information inside the same directory as the directory which stores all of the HTML files, however, I can't seem to get my head around for how to connect to this server. Furthermore, my initial approach was to use JS to connect, receive the data, and display the data on the page. However, that turns out to be unnecessarily complicated/unconventional.

I have gotten to the point that I have to use PHP to do all of the above, but I have no clue how to connect to db stored in the same directory. Furthermore, I didn't set any username or password when setting up the db, yet it seems like you require these fields when connecting to the db...

For this project, security is not much of a concern, so I don't really care about that. I just want a simple fix/solution regardless of the security/efficiency concerns etc.

I apologize in advance for having such a limited knowledge. Thank you in advance!