This is an H3, which should be used for topic headers

This is an h4, which should be used for sub topic headers

This is a p, which should be used for all content.

This is for content that goes on the left of the content right box. It should not be used unless there is a content right box. Otherwise the page will look odd and content will not know where to properly go. So use it sparingly unless you feel the great need to divide the page you are working on into two parts.

Additionally, only use h5 when you need to really bring a point home.
Content goes here and this is an h6 sized font.