Why does VS run the first file from a project?

Question

visual studio

Pressing F5 in Visual Studio starts executing the first file created in this project, which is not even open in the application itself. I myself do not write any big programs, but solve programming problems; in connection with which the question is: is it possible to somehow fix this or rewrite tasks in the same file, or to create new projects in VS to test them?

Answer 1

Right-click on the project "Make this project the default project"
It is the project that is not resolved

Answer 2

RMB on the project in Solution Explorer -> Set as StartUp Project