Log into Drupal.
Check the Moderation State in the yellow info bar to see that you are working on a Draft page.
Edit the page by clicking the Edit button in the lower right.
Scroll to the bottom of the editing page.
Choose Publish from the State (Change To) menu at the bottom of the page editing form.
The Moderation State should now show as Published.
Even if you start a new Draft of a Published page, the Moderation state for that page remains shown as Published in the top yellow banner because there is a Published page at that URL.
If you need to Unpublish a page to make it hidden from all public visitors, see Drupal 8: Unpublish & Archive a Web Page.