Most metas allow you to formulate your query with a syntax that is similar to the popular search engines and most have a Boolean option. There's a box for each engine, in which you enter search queries separately, using the appropriate syntax, and hit Submit or Search separately for each engine. Beaucoup Search Engines offers 14 engines in this configuration. Look for a meta that interprets your query into the engines' native search languages, or you run the risk of a less effective search that doesn't fully take advantage of query features. The answer makes difference in the processing time, and in how the results are returned.
Most meta results are relevancy-ranked.
Other results features vary greatly, but the most popular displays integrate the results from the search engines, and show which engines returned the hits. Most de-dup results. It seems a simple thing now in 1999, but searchers of traditional online services remember when de-duping across files was just a dream. Cyber411 returns results grouped by engine, but removes duplicates, providing a clean, usable list. Some display lists show only a brief title that links to a page, others display titles and descriptions very similar in appearance to what we find on search engine results screens.