Archives and libraries are centres of knowledge that support research and learning, and document and preserve cultural heritage. However, archives are rooted in a different tradition of information management, handling and providing access to information in a particular way. It is one that has emphasized the different roles of archives: legal, historical, administrative and cultural.
This archival tradition impacts how you access and use archival materials.
Records are viewed as a fonds, the totality of records generated by a person or organization throughout the course of his/her/its lifetime. The fonds is a hierarchical structure of groupings based on the ways in which the records were used. The highest level is the fonds, followed by the series, file and item levels. The fonds level gives the broadest view of the records; the groupings become increasingly specific.
A fonds, or fond d'archives, is the whole of the records, regardless of form or medium, automatically and organically created and/or accumulated by a particular individual, family, or corporate body in the course of that creator's activities.
A "collection" refers to a group of materials (irregardless of format) with some unifying characteristic. Within the context of special collections in libraries, the term refers to materials actively assembled with intent by a person, organization or repository from a variety of sources.
This is different from an archives, which is the organic accumulation of records and documents as the by-product of activities, where the origin and provenance and arrangment reflect their original order.
See the SAA glossary of terms for more information.
Available here: http://www.archivists.org/glossary/index.asp
There are two principles which govern the arrangement of an archival fonds:
Fonds are generally listed by the name of the creator (a person, organization or family). You can search for them by name. This is why it is important to note down names and titles during your preliminary research.
Original order is important to remember when you handle archival material. As a researcher you must always keep materials in the order in which they are found.