Any content that you want to appear on all pages like logos, copyright info etc typically goes in the layout.master file of your skin. All pages that use the skin will display the content. You can enter whatever raw html you want there.
Now suppose you have some content you have created in the content system, an instance of the Html Content feature for example and you would like to show that same content on all pages but you don't want to have to add it manually to each page in the site. You can achieve this once you determine the moduleid of the content. You can typically determine the module id when you mouse over an edit link you will see the mid= parameter in the url.
Once you know the id you can add it to all pages in the site by adding a ModuleWrapper control in your layout.master like this:
<portal:ModuleWrapper ID="mdl33" runat="server" ConfigureModuleID="33" />
where you specify the ConfiguredModuleID property with the moduleid of the content you want to show and the wrapper will load the content.
Be aware however, that content duplicated across pages is not good for search engine optimization.