Max 5 lets you add metadata to the various kinds of files in your Max search path. Metadata consists of information about a file you can attach to the file itself, but which isn't actually part of the file's content. The most common type of metadata you will see or work with is called a 'tag'.
Once you've added a tag to a file in Max, you can use the File Browser to search for all files in your search path that are tagged in a certain way.
There are several reasons you might want to add metadata to your files
The File Browser Preview displays a file's tags as well as author metadata. You can also use the File Browser to perform searches based on this metadata.
By default, the File Browser is set to display information about a file you select in its Preview pane, located in the lower part of the browser window. Depending on how your preferences are set for Max, you may need to enable viewing the Preview pane on startup.
Viewing metadata file tags

Adding metadata tags to a file
Note: a tag or author must be a single symbol (e.g. d-minor).
The tag will be added. and you will see the tag listed in the Preview pane.

Removing a tag from a file

Doing a file search using metadata
The File Browser will search for any files that have the specified tag, and display the results.