Begin by writing down a broad concept or topic in the center of the page, and draw a circle around it.
On a second piece of paper, make a list of as many words as you can think of related to your topic. Once satisfied with your list, separate these ideas into categories by how they are related to your initial topic. For example, if your topic was corn, categories might be recipes, nutrition, how it's grown, etc.
Draw a line coming out from the circled topic on your first piece of paper. Write down one of the categories and circle it. Do the same for the rest of the categories you came up with.
Draw lines radiating from each of your category circles and label them with the subtopics from your list. These may be characteristics, examples, or classes of the item within the topic.
Continue drawing lines out of your bubbles as you come up with new topics to relate or new connections you can make.