WordPress code reference is the documentation of all the code from the newest updates. You can click on links and it gives Description about what it does. It also gives a clickable link to the API's that are used to build WordPress web sites.
The function the_date will output the date of the current post , but only if it is different from the previous post. The function can be called multiple times, but if multiple posts are created on the same date, only 1 date will show up.
Parameters: all are optional
$before is a string
-Displays output before the date specified
$after is a string
-Displays output after the date specified
$display is a boolean
-Determines whether to echo date or return it
<?php the_date( 'Y-m-d', '<h2>', '</h2>' ); ?> * Displays the date using the ‘2007-07-23’ format (ex: 2004-11-30), inside an <h2> tag.
The WordPress code reference is a great source to help developers research functions. It also has documentation about the API's used on the platform.