A constructor is a method, which is called when an object 
of a class type is constructed, and it usually used for 
initialization. A constructor method has following 
characteristics:

It has the same name as class 

It has no return type 

It does not return any value 

Constructors are always public and we use them to 
initialize variable. 

There is default class constructor without parameter, 
provided by C# internally if we did not write any 
constructor. when ever compile that class,compiler create 
the default constructor(with out parameters).

In the other hand a Destructor is also called a finalizer. 
It is just opposite the constructor, it is a method called 
when the garbage collector reclaims an object. 

Constructors have following characteristics:

The name of a destructor is same as name of class 

The destructor declared with a tilde (~). 

Destructors are always public and never other than public. 

Destructors take no arguments. So, there is only one 
destructor per class. 

Destructors have no return type.