A few definitions:
A discovery service is a tool that searches all of the library's online holdings at once. It casts a wide net and is great for finding single articles or as a starting place for research. Primo is the discovery service that we use at Heritage.
Encyclopedias, thesauri, dictionaries, and almanacs are all reference sources. A reference source answers simple questions, or introduces you to a topic and summarizes common knowledge about it. Reference sources are great for helping you choose a topic, or learn enough about your topic to understand more complicated sources.
An eBook is a book that can be read or accessed through the internet. Some eBooks allow printing of sections of them, and many can be downloaded to be read offline. Most eBooks in the library can only be accessed online, the library doesn't have a physical copy.