Yahoo has commercial and noncommerical categories. One can submit to noncommercial categories for free, and one should do this, just don't expect a listing. If a noncommerical listing is very important you should browse to the appropriate category and click the suggest a site link at the bottom of the page. Submit again about every 2 weeks for as many times as you wish to until you give up or are listed. Remember most Yahoo traffic is via search so a directory listing will not really help you all that much to rank higher so its no big deal if you don't get the listing. Yahoo likes descriptions very short so keep this in mind and submit a description about the same size as the others in the category.

Submit an objective very brief description and title such as:

Domain.com - Topic

features news, reviews, and photos.

For commercial categories the process is the same except you have to pay a fee to be reviewed rather you are listed or not and every year you have to pay the fee again to remain listed. Unless your site can profit from a $299 a year fee for Yahoo directory traffic this shouldn't be considered. Keep in mind that most Yahoo traffic comes from search results and not directory browsing so your listing might not help all that much in generating a large portion of Yahoo traffic.