C# class without main method

Not all classes need Main method.

As MSDN States

The Main method is the entry point of a C# console application or windows application. (Libraries and services do not require a Main method as an entry point.). When the application is started, the Main method is the first method that is invoked.

There can only be one entry point in a C# program. If you have more than one class that has a Main method, you must compile your program with the /main compiler option to specify which Main method to use as the entry point.

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Only one class need to keep the Main method, the class which acts as entry point of the application.

The signature of the main method is : static void Main(string[] args) or static void Main() or static int Main(string[] args) or static int Main()

Check out this link for more details : Main() and Command-Line Arguments (C# Programming Guide)

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For your above example:

public class MyClassName // changed the class name, avoid using the reserved keyword :P
{
    int stuff;
    public MyClassName(int stuff)  // is the constructor
    {
        this.stuff = stuff;
    }
    public void method()
    {
        stuff = 1;
    }
}

If you need to use that class, you can create a static class with main method:

class ProgramEntry
{
    static void Main(string[] args)
    {
        MyClassName classInstance = new MyClassName(2);
        classInstance.method();
    }
}