In the design process, mind mapping is visual brainstorming: You look through all ideas that come to you, with no criticism. And you don't just write these ideas down but connect them together to get new associations.
How to Start
Write the main subject in big letters: "Website for a Spanish language school," for example. Then start branching out and add "Design," "Structure," and "Mood". Try to come up with your associations for each idea.
Write down every thought, even tiny ideas about button copy or menu style. They'll help you develop your main idea and create a complete picture of your website.
How to Capture Ideas
Use different colors, add arrows and bubbles, circle, and underline words as you like. Try to visually organize thoughts and connect them with those you've already written down. If ideas come to you as images, just draw them, it'll stimulate more creativity.
Add between 1 to 3 keywords for each branch. Words evoke more associations than phrases.
Take a little break, then go back to your diagram, and read what you've written. Add new ideas and associations, select those you like best, and think them over. In this step, you are quite likely to either get the right idea to accomplish your task and get inspired to create a design or choose what to reflect on next.