Painter comes with default libraries of Art Materials and additional libraries that can be found on the installation disk under the Stuff menu. New libraries can be created. This is particularly useful as a person starts developing new materials so that the default libraries don't become overly cluttered with custom materials.

For the example here, we'll create a new Pattern Library. 

To do that, click the Pattern Section Menu triangle (at the right of the palette).  Pick the Pattern Mover. This will bring up the Mover menu.

 
Choose New. Type a name for the new library. As a caution, pay particular attention to the folder Painter wants to save to. Painter has a bad habit of remembering the last location where a file was saved and use that for the default library directory. It's best to store new libraries directly underneath the Painter directory. Quit.
The Mover menu can also be used to move items from one library to another by dragging between them, but that doesn't need to be done right now.  
Open the library by clicking the menu icon (the white bar under the pictorial pattern icons that identifies which pattern is in use, Overlapping Waves, in the example at left). This will bring up the menu at right. Click Load Library. The new library that was created above can be loaded. (As with the caution above, it may require changing directories to find it if any files have been opened or closed since creating the new library).

New files can be added to the library.