For the last few years, since RDA has been in the making, there has also been talk about MARC’s demise. That’s MARC as in Machine Readable Cataloging. As our metadata evolves, the way to transmit it will probably also evolve. XML is a possibility, but for now we have MARC. MARC codes have recently been updated in anticipation of RDA.
If you have problems understanding all those codes, or just need to check out one(s) that you don’t use very often, there are some good sources available.
Understanding MARC Bibliographic is the best quick and easy MARC reference I’ve ever run across. If you want a copy in your hands, it is available from either Follett or Library of Congress for $5.
Library of Congress also hosts the official MARC21 Format for Bibliographic Data. After you click on a tag, you will have the choice of seeing the “full” or “concise” version of the description.
I’ve always preferred to use OCLC’s Bibliographic Formats and Standards . BF&S is freely available on the web; you do not have to be an OCLC member to use it. Perhaps it’s because I began using the print version of BF&S so I was familiar with the text and layout, or perhaps because I’m more used to it than MARC21 Format. I find it easier to navigate from one tag (or subfield) to another.
MARC uses codes for Geographic Area, Country, and Language. All are available on the official MARC21 site. When it comes to these codes, BF&S (eventually, after a few clicks) leads to MARC21.
If you’d like to practice by using a tutorial, there are a couple available. MARC21 Tutorial is from the University of Southern Mississippi and based on Understanding MARC Bibliographic. Introduction to the MARC System is one of several free cataloging-related tutorials offered by Idaho's Alternative Basic Library Education (ABLE) Program. Be careful, though as the ABLE program is slightly out of date. Maybe that’s a good test: See if you can find the obsolete indicator.