The .NET Framework provides a run-time environment called the common language run-time, which runs the code and provides services that make the development process easier.

Value type: The content of a value type variable or constant is simply a value. For example, the content of the built-in value type, int, is 32 bits of data. Its contents in memory is allocated on the stack. We can define a custom value type with the 'struct' keyword.
public struct Point { public int X, Y; }
Reference type: A reference type has two parts: an  object and the reference to that object. The content of a reference-type variable or constant is a reference to an object that contains the value. A reference type, such as an instance of a class or an array, is allocated in a different area of memory called the heap. We use 'class' keyword to define it.
public class Point { public int X, Y; }

Method overload defines use different type of parameters with  same method name or different set of parameters is known as Method Overloading.
void Foo (int x);
void Foo (double x);
void Foo (int x, float y);

Stack: The stack is a block of memory for storing local variables and parameters.The stack is always reserved in a LIFO (last in first out) order;
The stack is important to consider in exception handling and thread executions.Heap: The heap is memory set aside for dynamic allocation. You can allocate a block at any time and free it at any time.

In C# ref modifier is used to pass arguments by reference.
Out: An out modifier is like a ref modifier except it need not be assigned before going into the function.
Params: The params modifier may be specified on the last parameter of a method so that the method accepts any number of parameters of a particular type. The parameter type must be declared as an array.