WordPress' search function allows for users to search for keywords or articles instead of clicking through each page trying to find a specific post. The search will parse through the titles of posts and/or pages and those related to the search term to find what the user is looking for.
The URI plays the role of specifying the search parameters. The search query keywords are displayed in the uri as the default "/?s=searchwords" in WordPress; 'searchwords' being the search words of the user input.
Showing the active search term and the number of results is done through adding some code to the 'search.php' file. The code and an example are included in the link above.
Searching with the WordPress search bar is quite simple. Despite not being the most efficient serach form, it gets the job done and is easy to implement along with a ton of resources that help developers implement ways to make it more efficient and effective.