What is object in IClass obj=new Classs()

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C#

which one create object and which on create memory
in this sentence
1. Class obj=new Class()
Class obj= create object
and
New Class()= create memory
is it correct?

2. IClass obj=new class()
which one create object ans which one create memory


3. Mainclass obj =new Derivedclass();
How the object will create and memory management will work