Some themes can include content from modules as “widgets” (like a sidebar with a project listing that is visible on every page) but pages themselves can also include content, allowing you to do things like create a “Projects” page. Project sections (aka. categories) let you to categorise your projects and by using the powerful Page Type option, you can create separate pages for the different categories of work you produce: for example, a Print, Web and Music page.
Under the Page Type section on the page edit screen, you can specify the type of content to include, in this case Projects, and then use the Options field to specify which project section to include, by entering:
section= print (or web or music, etc)
Multiple options can be used, by entering a comma-separated list (option1= value, option2= value, …). This gives you total - and flexible - control over how your website behaves, with minimal effort.