You may be familiar with Plone's content types and how to add content to your site. If not, please read Chapters 4, 5, and 6 of "Practical Plone 3", Veda Williams, Packt Publishing where this subject is covered in detail.
Often, it is necessary to add additional content types to provide a particular functionality. This is not to say adding a new content type is always a good idea, but some problems are particularly well-suited to being solved with the addition of a new content type.
For example, some folks like to blog with Plone. One of the simplest ways to start blogging with Plone is to use the Scrawl add-on (Products.Scrawl package), which creates a new blog content type (by copying the news item content type):
You can easily add the Scrawl add-on as follows. In 02-site-basics-blog.cfg, we have:
[buildout] extends = 02-site-basics-dropdownmenu.cfg [instance] eggs += Products.Scrawl
Now stop Plone (with Ctrl + C or Ctrl + Z/Enter) and run Buildout...