To find out the WordPress version, you must access the administration panel of the installed WordPress.

 

Once inside, go to the "Dashboard" column and then click on "Updates":

In this section, all update notifications for your plugins and themes will appear, but at the top you can also see the version installed on that WordPress:

It is recommended to always keep track of the WordPress version you are using, as many plugins and themes are only available up to a certain version, which may cause compatibility errors if they do not match.