Libraries contains components (=devices) to use with the SchematicEditor. Beside symbols and simulation information it may include all information on its layout. This can be a link to a existing design or link to a macro which create a parametric design. In the Integrated Circuit design libraries are often called Physical Design Kits (PDK) and shipped be the foundery as it contains process spezific and confidential information. Here are public libraries available for the LayoutEditor / SchematicEditor:
ParametricShapeLibrary with non electrical shapes like alignment marks,
OpenCellLibrary an Integrated Circuit PDK for education and demonstration,
discretes a library with some discrete PCB devices,
transitors a library with some PCB transistors,
sources a library with power sources,
simulation common simulation commands runing with different simulatior.