By default WordPress has a search built in. Any search performed on a website ends with a
?s= query parameter. In your address bar one can see something like this:
It’s really useful to keep track of search using Google Analytics. In order to do so, go to Admin (cogwheel bottom left), View Settings -> scroll to the bottom.
Enable Site search Tracking and put an
s for the query parameter. Check the box
Strip query parameters out of the URL. Follow this screenshot for guidance: