Title blocks define the size and appearance of a drawing sheet. Think of them as templates for the drawing sheet. You create a title block family using the Family Editor. For each title block, you specify the sheet size and add borders, a company logo, and other information. You save the title block family as a separate file with an RFA extension.
Typically, you create custom title blocks and save them in the following location: %ALLUSERSPROFILE%\Autodesk\<product name and release>\Libraries\<language and locale>\Titleblocks. You then add these title blocks to a default project template, so they automatically load when you create a project.
Tutorial: Working with Titleblocks and Sheets