By default, a user that is not logged in that enters the URL of the site will be redirected to the logon page. If you prefer you can present information to a user about the system, such as what it contains and how they can get access.
Go to System settings and choose the Public home page option and you will be able to enter the HTML to be used in the middle part of the page when a user visits the site and a stylesheet that will be applied to this HTML.
Note that you can only use a maximum of 4,000 characters for this HTML, although this will normally be sufficient and you can always use a frame if you need more.
If you make changes to the stylesheet then you will need to click on the Apply button before the changes are applied to the HTML. You may want to open a new incognito / private window and navigate to the home page to see what it looks like when you are not logged in.