where do i insert the codes in here: namespace BankSystem { public class Startup { } }

In the C# language, you can insert your code inside the class Startup. Here is an example:

namespace BankSystem
{
    public class Startup
    {
        // This is where you can insert your code
        public void YourMethod()
        {
            // Insert your code here
        }
    }
}

In this example, YourMethod is a method where you can insert your code. You can replace YourMethod with any valid method name and add parameters if needed. The comment // Insert your code here is where your code should go.

Remember, the code you insert should be valid C# code and should be relevant to what you want your Startup class to do.