"The MARC formats are standards for the representation and communication of bibliographic and related information in machine-readable form" (Library of Congress website).

Bibliographic Formats and Standards is an extensive guide which outlines input standards for bibliographic information contained in WorldCat records, subdivided by fields. "It provides tagging conventions, input standards and guidelines for entering information into WorldCat" (OCLC Bibliographic Formats and Standards Website).

Here is information from the Library of Congress about MARC records entitled Understanding MARC.

Here is information from the Library of Congress about MARC records entitled MARC 21 Concise.

OCLC Bibliographic Formats and Standards is another online MARC resource.

The Library of Congress online catalog can be used to view MARC records. After you conduct a search and retrieve a catalog record, click on the "MARC tags" tab to see the MARC record.

The MARC website is a good place to start to find MARC records. There is also a listserv you can join or simply search the listserv message archives. Listserv topics include cataloging fields for ISBNS and DOIs and cataloging in different languages.

Read the appropriate chapter of AACR2 and determine which elements of description are required. Then go to OCLC Bibliographic Formats and Standards at http://www.oclc.org/bibformats/ and determine the MARC fields that correspond to the required elements.