Styles are managed in the Styles browser. Here's a few tips for working with styles...

Heads Up! Every time you click on a new style it is added to your model, and will continue to travel with your model. This can increase file size. Click on the context arrow and choose "Purge" to delete all styles that are not in use, or saved with a scene.
Heads Up! Many style properties are available in the menu dropdowns at the top of your screen. Keep in mind that you can change a style's properties without being in the Styles browser. While it's possible to change the properties, you must click the update button in the Styles browser to save them.
After you have created some styles, you can save them to a new library by following these steps...
Dig Deeper! Read more about professional SketchUp Workflow styles collections on page 149 of "The SketchUp Workflow for Architecture".