The “Hello World” post in WordPress is actually just a simple dummy post content set by the WordPress as a placeholder post content upon initial installation.
Post installation and initial setup you can simply trash the posts and start creating your own posts for your website from Admin Dashboard > posts.
Please refer to the link below for any further reference :
The text you are referring to is the default instruction text used by the theme for users roles that can publish posts while no contents are found in the site.
The message is not shown to the site visitors who are not logged in to the dashboard. Thus, you can start creating contents for the site and the posts created will appear on the page.
You can also display your desired contents in the front page by setting “A Static Page” in the front page by creating a page and setting it in “Front Page” option from your Admin Dashboard > Appearance > Customize > Static Front Page.