A domain consists of the last part of a URL (web address) that ends in .gov, .edu, .org. Additional domains include .com.
The Google search engine supports the ability to limit a single keyword or longer Boolean search to just one specific domain such as .edu. This makes the search itself a quality filter. At present limiting your internet search to just one domain can only be done in Google.
Review the handout and immediately practice the techniques shown. You should be seeing better results that will require less effort to evaluate as to their authority.