The listings are organized as a subject tree or subject directory, that is, a listing of subjects organized into categories, which are usually arranged hierarchically. Directories rely on the judgment and expertise of the people compiling them and it' s not hard to see that subject experts would have different selection criteria than a hobbyist or casual user. Listings may be submitted to the directory for possible inclusion, or chosen by the indexer. Whether or not your site is included in the database is a function of how relevant it is to the subject matter of the directory, its scope, coverage, and accuracy, in additional to other selection criteria such as audience. They traverse the web site content and its links in a variety of different ways and collect the results into a database.
Webmasters can also submit their sites for possible inclusion into the database.
So frequently it is only a matter of time before your new site gets indexed by one of the major search engines.