Mindmapping is a way of showing the relationship between concepts by means of a drawing - it is sometimes also known as "spider diagrams". This website uses mindmaps extensively -for an example, click on the picture in the top right corner of the screen. The technique and use of mindmapping has been described in a number of books by Tony Buzan. Mindmaps are supposed to have a central concept to which everything else is related; similar diagrams, which have no one central concept, are known as "concept maps".
The visual nature of mindmaps, or concept maps, makes them particularly useful at an early stage of work on an essay, when you are defining the problem and producing a plan, because they help you form a mental picture of the topic. They work best for a relatively limited number of concepts, and don't help in ranking the importance of your various ideas, so at a later stage when you are planning in more detail, you will probably want to use outlining.
Since mindmaps are designed to be rough sketches which get revised frequently, you might find it easier to use a computer program to do mindmapping, rather than have to redraw the mindmap every time you make an alteration. You can download the following programs for free:
The mindmaps on this website were made using Axon Idea Processor.