Some search engines choose the sites to show you based on popularity. While they may be popular these sites may not contain valid information. The user must determine a sites validity. The search engine is not responsiblr for this. For example, Twinkies are popular, but they are not nutritious no matter who gives them to you.
Some search engines accept money from makers of web sites.
Theresore, they show you the sites of the people who pay them more first. This too, is not a good way to select a site. A meta engine is a collection of search engines. Rather than having just one program search the Internet, a meta engine is a program that enables many search engines to look at once. Directories are collections of web sites, usually assembled by real people who have actually visited and ranked the web sites.