Within your DNN site, each module has a menu for MODULE SETTINGS.  You access the module settings by going into edit mode and then on the module, hover over the gear wheel of the module and click on settings

The TITLE field

It’s recommended that every module have a unique title, this is super helpful when you “adding existing module”.  Without a module title, the default is either “enter title” or simply “text/html”.  The unique title makes each module easily identifible and relates to the content it contains.

DISPLAY ON ALL PAGES option

 Just like the name says, use this option for content (like the footer) that needs to be the same across the whole site.  It will literally be added to every single page, including admin-only pages, registration pages, etc.  So you may need to go back through some pages and remove it where it doesn't make sense.

Permissions
Like pages, modules can be visible to only specific roles.
Default is for the module to inherit the permissions from the page settings, so if the page is visible to All Users, then the module will be too.  

Page Settings Tab
If needed, this is where you specify a “container” for the module to use.  Containers have some inherent styling that will apply to the content.  If you are not familiar with your site's containers, then ignore this field or ask your website's developer.