How does brainstorming technique of mapping in writing a research paper

You can put anything into a circle. It' not for marks (usually), so no one will see it but you.

You can organize the body of your paper. Points underneath the main circle give you a hint which way you should try to look up information. 

You can erase certain things because they are irrelevant, or you can't find information, or the information is too complex to be of much value. 

Sometimes a topic is overwhelming. You have to look up information on the information you just found and it's not suitable for 500 words. For example you are asked to write about an experience that influenced your life the most. Let us say it was a visit to the doctor's office. He gives you a written report of what he found. You find that it is so full of technical terms that you have no way of writing why it influenced you so much. You are too busy trying to get to the bottom of the jargon. 

Finally mapping points at material you really do want to write about. It also lets you look at the tone you are going to use to write it. There's no harm in trying a few sentences to see what it sounds like and putting them in large circles underneath your original circles.