Mind-map is the plan you make in your mind before doing anything. Now when you are going to attend the class you try to make your mind about the way you will record lecture by taking notes. Similarly everyone makes mind beforehand in order to do something so that he / she may do it in a best possible way.
Suppose Cynthia and Jessica are going to attend the lecture on western philosophy. Cynthia is carrying a notebook and a pen with her and she has planned in her mind the ways by which she could record the lecture best possibly. On the other hand Jessica had no pen nor notebook because she had not planned in her mind quite well before time, or even if she had she needed to make at lease some plan to work upon in order to gain much in less time. Now tell me who will get the better understanding of the lecture? It is of course Cynthia just because she had some mind-map to work upon.
Now you know mind-map is important because there is a great difference in proceeding with or without it.
Example and method of mind-map
Suppose you are going to deliver a lecture on pollution. First you make plan in your mind (mind-map) and then you implement it in the class. Now what are those questions that are likely to be there in your mind before you made a plan are as follows.
Now mind-map is the answer of these questions. Immediately after that you start to create a map in your mind that is the systematic organization of all things necessary in the lecture and that facilitate your talk in the class. That map in your mind will be something like this.
It means you are thinking in terms of the points mentioned in above map in order to organize your lecture and which are explained as follows.
You first have to determine your arguments.