WordPress code reference is a developer resource dedicated to referencing WorPress code. It has multiple filter options that allow you to search for code like functions, methods, classes etc.
As the parenthesis allude to the_date is a WordPress function. It returns the date a page was published. And is used in the WordPress loop. It appears that there is also a the_date filter hook that filters the date a post was published for display. And also a get_the_date() function that looks like it does the same thing as the_date().
the_date accepts 4 optional parameters ($format, $before, $after, and $echo). The $format parameter specifies how to display the date. If not included WP gives the WordPress default formatting. $echo tells WordPress whether to display the date or to return it.
The WordPress Code Reference is a good resource for developers, but it's no MDN for sure. Example would be helpful, or just better explanations. I spent a lot of time looking into this function, and to be honest I still don't know anything other than it returns the publish date of the current post in a loop. Other than the $format parameter, and somewhat the $echo parameter, I don't really know what the parameters listed actually do.