1 A normal library (like the international library) contains mostly a lcf-file (Library Container File) and folders with textures, databases etcetera. You just load the entire folder in the library manager (for instance ArchiCAD Library 12 in the Graphisoft/ArchiCAD 12 folder).
When you are looking for extra libraries, you can buy them and load them with the library manager. Also you can load single objects (gsm-files). A lcf is nothing more than a collection of gsm-files. These single gsm-files are widely available on the web, for instance the
object depository.
2 Image files you can load similarly as single gsm-files.
Preferably you create a single folder with you project (a project library) and there you place all your images, downloaded objects and self-created objects. So you can load just this folder and have them all.