The search settings page provides the ability for you to define which ad fields are searchable.
by ID - this uses the database's listing ID number which is roughly the date in which the ad was placed (exceptions include directly modifying the database.) Ascending will be from 1 to X (or roughly oldest to newest.)
by Title - this will place the search results in alphabetical order by the Title's first character. Ascending is from A to Z with numbers (1 to X) appearing ahead of letters.
by Description - this will place the search results in alphabetical order by the Description's first character. Ascending is from A to Z with numbers (1 to X) appearing ahead of letters.
by Featured - this will place the featured ads at the top of the search results when DESCENDING is used. All the featured ads will appear first and then standard ads will appear. Within each group (featured and standard), the ads appear by the date the ad was placed from newest to oldest.
by Price - this will place the search results in order by price. Ascending will be from least expensive to most expensive.
by Hitcount - this will place the search results in order by the number of times an ad has been viewed (popularity). Ascending will be from least popular to most most popular.
by Date Added - this will place the search results in order by the date the ad was placed. Ascending will be from oldest to newest.
by Expiration - this will place the search results in order by the date the ad is scheduled to expire. Ascending will be from oldest to newest.