Question

public delegate void ExecuteCallback();

class Executioner
{
private ExecuteCallback _doExecute;

public void AddMultiple()
{
    // Add a delegate to MethodA
    // This will work even if _doExecute is currently null
    _doExecute += new Execute( MethodA );

    // Add a delegate to MethodB also
    _doExecute += new Execute( MethodB );

    // Add a delegate to MethodC also
    _doExecute += new Execute( MethodC );
}

public void MethodA()
{
    //...
}

public void MethodB()
{
    //...
}

public void MethodC()
{
    //...
}

}

Answer 1

+= is usually called the “addition assignment operator” but in the context of delegates…

The += operator is also used to
specify a method that will be called
in response to an event; such methods
are called event handlers. The use of
the += operator in this context is
referred to as subscribing to an
event.

Taken from MSDN documentation here.

How to: Subscribe to and Unsubscribe from Events