Find out what page as start page

I downloaded a vb.net sample.
There are many folders under project as sub-project.
Once I open sln file and run it, all folders display on the start page as buttons.
How to find out which page is start page?
I tried to find out prom property form the project but no more info.

You talk of pages (and have ASP in your name), yet you also talk of this being a .NET project. Is it a windows app or is it a web forms app?

This is a windows app.

Then go into the Project|Properties menu and take a look at the startup object listed on the Application tab. That is the start form if it is a form. If it is not a form then there is no start form. All Windows apps technically start at a method (Sub Main), you just won't see that method if you have a start form set.