Sir it is really very simple, I had never done a single work on my car myself.
For this, your car must be cold. Overnight chor kar subha Karen tou behtar hai, gaari halki si bhi garam na ho.
Feel under your car's radiator from below. If your radiator os genuine or good quality it will have a drain plug. Get a drain pan or any old dish (that you will never again use because rust is toxic) and drain the water from below. Then add water in radiator and repeat the process 3-4 times until clear water comes out from below. Then add fresh coolant/battery water.