A Class in C# is a virtual entity or a blue print or a template or a model. A Class will not occupy any memory in than RAM.

Class Syntax:

AccessSpecifier class <ClassName>
{//Class body starting.
   //Class related code.
}//End of Class body.

Note: Let's try to understand AccessSpecifiers or AccessModifiers topic later, as of now let's use public access specifier.
Note: User can use any ClassName.

Sample Class:

public class Doctor
  public string name="dr.rajeev";
  public int age=36;
  //a class can contain data members and behavior's.

Understanding class:

Let's try to understand what exactly a virtual entity or a template means, and why we call class as a virtual entity.
When the following code is sent to C# compiler it will compile all the code. But CLR will not execute the code. Hence no memory will be created for storing data present in the class. For more details see the following diagram.
Note: A class will usually contain data members as well behaviors (methods). Declare variables for storing data and create method for performing actions. Let's talk more about methods in the Methods tutorial.
Assignment: create a class with the name Patient and store following patient details.
name: Paul age: 38 disease:diahria gender:male (create boolean variable for storing gender).