Go to Basic Site Settings via Configuration > Basic Site Settings (/admin/config/system/site-information)
On this page you can change many of the global site settings available to you.
You can change your site name, give it a slogan or update the site email address.
Additionally, you can provide a parent organization and link which will display at the top of the website on the header for websites using the "Display below IOWA bar" site name display option within theme settings.
You can make any existing page the front/homepage of your site.
Enter the page’s URL path alias (e.g. /home) or the permanent node ID path (e.g. /node/1)
Note: You cannot delete a page that is designated as the front page.
There are default "access denied” and “page not found” pages, but if you want to customize the message, create the page(s) first and assign them here.