what is the meaning of ~ProcessQueue() ?.. im asking about the tilde

You must have created a constructor by name ProcessQueue() within the class ProcessQueue. When you write ~ProcessQueue(), it calls the destructor. A destructor is a special method that releases the instance of class. The destructor is called only when the object is no more required.

Note: The .Net framework automatically cleans up the memory used by the class even when you don't call it.

This is a destructor.
You may read this to understand how it works in C# (since destructors in C/C++ are sligthly different):
http://www.c-sharpcorner.com/UploadFile/chandrahundigam/UnderstandingDestructors11192005021208AM/UnderstandingDestructors.aspx[^]

Class have a constructor.
When we create the object of a class at that time constructor are used to initialize the object. Every class must have constructor.

Symbol ~ is indicate the destructor. It works opposite the constructor. It free the memory used by the constructor in initialization.

CONSTRUCTOR: sum();

DESTRUCTOR: ~sum();