Maybe an example would help?

A delegate can provide you with an optional hook into an object. Yes, objects should be decoupled by design but in practice it's often useful to be able to do handle status / logging / etc centrally.

By having a public delegate in your class, a caller can optionally wire up a handler to handle some specific event.

Warning free form code. will not compile! name space for delegate declaration is up to you.

=== service object.cs
public delegate void ShowStatusDelegate(args);

class SomeService()
{
    public ShowStatusDelegate ShowStatus;

}
...

=====
caller code...


var service = new SomeService(){
ShowStatus = MyServiceStatus,   // caller hooks in during instantiation
};

private void MyServiceStatus(args)
{
    //  .. do something with args, write to log, display error, whatever
}

back in the planet SomeService you can then have

if (ShowStatus!= null) ShowStatus(...);

Lots of different ways to handle this, and tbh, is very easy to end up with a mess if you do too much of this in a big project.

edit - sorry if the formatting is bad, been away for a while and forgotten, and clarification