If you’re looking to renew your knowledge of Dewey Decimal classification–which can be a drag, but plenty of libraries continue to use it and it’s a good skill to retain over the long haul–then you might want to take a look at the WebDewey Tutorial over at OCLC’s web site. They cover Dewey in a fair amount of detail. From the web site description:
WebDewey offers easy-to-use, World Wide Web-based access to the Dewey
Decimal Classification (DDC) and related information, with searching
and browsing capabilities; Library of Congress Subject Headings (LCSH)
intellectually and statistically mapped to Dewey numbers; and links
from the mapped LCSH to the corresponding LCSH authority records. You
can also add your own notes to WebDewey and display them in context,
which allows you to both record valuable information about local
classification practices and have it available for ready reference.
The only problems that I can see is that the tutorial won’t work on any Macintosh or UNIX system and it’s selective as to which PC browsers it works with. You may have to tweak your preferences a bit.