How to get started with back-end development (very beginner) [on hold]

I'm starting to learn web development to get a job at my city but I'm feeling lost. I have learned basic front-end (basic html, css and javascript) and now I want to learn back-end but I have no clue how to connect the front-end websites I have created with a back-end.

What I need to know is how to get the information I have on my html websites and connect them to a database using a back-end language like php or C# (I need to learn these two).

What do I need to learn first? Whats the best way to learn web development.

I tried watching tutorials on C# .NET MVC but it feels like people are building the websites from scratch and not just adding back-end support to an existing front-end website..

Thanks!