Migration from .net 5 to 6 documentation not clear

Question

I have an application to migrate from .net 5 to .net 6, but I don't really get the MS documentation. It says we should transform the two Startup.cs and Program.cs in one Program.cs file but is unclear what kind of content should it have.

say we have

Startup.cs:

using ...

namespace WebAppRPv5
{
    public class Startup {...}

and

Program.cs:

using ...

namespace WebAppRPv5
{
    public class Program {...}

The documentation states (picture bellow):

not clear what is this code, where should it be, in Program.cs? If that, where is the namespace, the usings, the main entry class?