1 - Same method name.

2 - Number of parameters should be different.

3 - Types of parameters should be different.

To implement the method overloading, the methods must have same name and the numbers of parameters or data types of parameters must be different, having different return types of method does not make the method overloaded. 

Example

using System;
namespaceMethodOverLoadingConsoleApplication
{
    classMethodOverloading
    {
        /// <summary>
        /// mehtod area(int side) for calculating the area of square 
        /// </summary>
        /// <param name="side">side of square</param>
        publicvoidarea(intside)
        {
            intz=side*side;
            Console.WriteLine("Area Of Square : "+z);
        }
        /// <summary>
        /// mehtod area(int length,int width) for calculating the area of rectangle
        /// </summary>
        /// <param name="length">length of rectangle</param>
        /// <param name="width">width of rectangle</param>
        publicvoidarea(intlength,intwidth)
        {
            intz=length*width;
            Console.WriteLine("Area Of Rectangle : "+z);
        }
    }
    classProgram
    {
        staticvoidMain(string[] args)
        {
            MethodOverloadingmth=newMethodOverloading();//Create object 
            mth.area(4);
            mth.area(7,5);
        }
    }
}

Output :

Area Of Square : 16

Area Of Rectangle :  35

In this example, i have created two methods with the name area() - one for calculating  the area of square and another for rectangle, note that both the methods have same name but different  number of parameters which make the methods overloaded.