It is use to free the memory of the object r method in use.

leakage memory of unused and unreferenced objects

it is clr function 
it is use to release those objext whitc is not longer useor 
no longer refeances in application 

it is System.GC.Collaction

garbage collection is the process of clearing the memory of 
unused objects, which will be taken care by CLR on 
periodical basis.

Actually the new operater is used to allocate the memory to 
an object that object not needed for longtime,so that 
objects are thrown away or release from the memory by the 
garbage collector.

Ofcourse, Garbage Collection is done for the memory 
utilization (making use of memory space which is allocated 
to the unused objects).
And this Garbage Collection is autometically done by the 
CLR. Still we can also implicity for the CLR to collect the 
unused memory allocated to unused objects. But that is not 
at all necessary.

When a program is loaded into memory, it is organized into 
three areas of memory, called segments: the text segment, 
stack segment, and heap segment.
So the compiled code will reside in the text segment.
the variables like string, int ect..(value types) will 
reside in stack segment.
the objects like class(reference type) will reside in the 
heap segment.
So when a new object is created the Garbage Collector will 
look unused objects and it will free them from the heap. so 
that the new object can reuse the memory allocated to the 
unused object.