A dummy is essentially a way to keep and store inspiration, ideas and thoughts. My dummy's are often Moleskin notebooks (blank paper). I prefer a neutral dummy (black, brown) with a reasonable size. Big enough to draw and sketch in, small enough to carry around.
Using a dummy can become really 'addictive'. You'll find yourself going everywhere with the dummy, putting it next to your bed when you're going to sleep, writing, drawing and doodling when you have the time to. But that's a good thing, it means you're 'doing it right', you're utilizing the concept of keeping a dummy.
One thing I had to learn about the use of a dummy, is to not set expectations or limitations. I'm naturally a bit of a perfectionist and I like my things to be structured and organized. A dummy isn't supposed to be 'perfect'; because that would mean that there are good and bad thoughts, ideas and inspiration. A dummy is the ideal place to let go, write everything down, draw (even if you feel like you can't), be creative, be messy and open-minded. Also, don't be harsh on yourself when you've had a couple of days (or weeks) without any ideas or thoughts for your dummy; that's perfectly fine, you'll get new ideas or inspiration sooner or later.
If you're in school, if you're creative or if you want to experiment with your creativity and thought process; buy a notebook (preferably with blank paper), and start to write down any ideas or thoughts you have. Draw, doodle or sketch what's currently on your mind and paste anything that inspires you into your dummy. Not only is it a great way to keep track of your ideas, it's a good way to feed your creativity and see how your thoughts develop over time.
Let me know where or when you get ideas! @catiemccartney