In your Dashboard go to Pages, click edit for the page you want to edit (in this case the page that is set as your homepage). Now, in the editor, type your content into the page and click Publish to save.
If you are using a plugin to create the “announcements” content, the plugin may have either a shortcode or a block that can be used. For this you should look into the plugin’s support/documentation/help for more information regarding how to add it to a page.