The default library can be easily extended with new libraries or with your own symbols. To add new libraries, use the Add Symbol Library command under the File menu, choose the folder that contains HighDesign symbols and select the destination folder.
To add your own symbols, you can use New Symbol command in the Tools menu to create a new symbol and add it to the User Library.
Alternatively, you can use the Symbol Inspector to create, edit and rename sub-folders, and create symbols and views from a selected drawing by using the buttons on the lower hand side of the panel.