404.php is the page that shows the warning message when end user tries to go to a page that doesn't exists, for example:
http://localhost/topcat/page1234 as you can see in the following image:
Here, we first search for the term (# 1), and then we get the message (# 2). Below the message, we get the search box (# 3)—same one as in
search.php—so we can search for something that exists in the system, as maybe, we have misspelled the page. Below that, we see some other widgets (# 4)—Recent Posts, Most Used Categories, and so on—that will give us more options to find the stuff that we are looking for. So, at first, we should change ...