c – How to debug a single file in Visual Studio 2017?

Hello, I am a beginner in programming, I program in C in VS 2017.

I would like to know how to debug a single file. I have a project, with two files A and B, but when I press F5 to debug the B file, it just debugs the A that I created first. How to choose to debug only B separately?

Thanks in advance!