The yellow pages are organized into categories- each section is a category someone would want to look up phone numbers for, mostly businesses selling similar products. For example: restaurants, plumbers, lawyers. The topics are organized alphabetically.

When you want to look up something specific, like places to order pizza, think of categories that might describe it. There might be a "Restaurants" category, but "pizza delivery" is popular enough that it may have its own section. Once you have a category in mind, find it by searching the book alphabetically; if you need more information about that, maybe gwern can help (see gwern's comment).

Once you have found a relevant section of the yellow pages, you will see a list of names and phone numbers, as well as some paid advertisements, also with names and phone numbers. Every entry in the section is a member of the same category. Then pick one entry and call.