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There's no better way to learn how to use Paint Effects than to get some hands-on training designing a custom brush. Once you have practical experience working with the many settings available for Paint Effects brushes, you'll have a much easier time working with the brushes listed in the Visor.
When you create your own brushes, most of the time you'll start with one of existing brushes available in the Visor and then edit its settings until you get the look and the behavior you want. For instance, if you want to create a creepy nerve growing in a test tube, you may start with a brush preset that looks similar to what you want, such as a tree branch, and then experiment with the settings in the Attribute Editor until the branch looks and acts like a creepy nerve.