Unless you're doing a monochrome masterpiece, you need colour to work with. Pick a colour and then the shape, fleck, or tool that you want to use.
Pick from the presets, or create your own using the colour picker and save it for future use. Each group has a ready-made tumbler colour.
Those are the ones with sections of different shades. They behave differently depending on the tool used, but also on whether they are static or spinning.
For example, with smear shape, a static tumbler will change with each separate smear, but a spinning tumbler will change dynamically as you smear.
The Dreams User Guide is a work-in-progress. Keep an eye out for updates as we add more learning resources and articles over time.