Many sites have in-site search. Visitors can type in a keyword in a search box and find relevant information within the website. For a site owner, you might want to know what people search for on your site. Google Analytics Site Search can do exactly this for you.
If you already have Google Analytics set up for your site, follow this page to enable the site search. (Tip, if you have a Word Press site, simply enter “s” as query string for step 5 in the instruction.)
Otherwise, start by signing up for Google Analytics.