How to raise event in a separate class?

Question

I have a class:

Class A
{
    public void EncodeMessage(object sender)
    {
        //Handle the Message received event
    }
}

Another class

Class B
{
     Message comMessage;

     public void RegisterForComMessageChange()
     {

     comMessage = ExtractComFromShcMessage();
     message.MessageReceived+= EncodeMessage; 
     //How to bind the message received event of this class to the event handler of Class A (i.e EncodeMessage)?

     }
}

How do I raise the register for an event in a separate class from that of the event handler?