One of the most common and most used capability is starting a paragraph. There are a number of different types of paragraphs, any of which can be initiated with macros supplied by the macro package. Normally, paragraphs start with a blank line and the first line indented, like the text in this manual. There are also block style paragraphs, which omit the indentation:
Some men look at constitutions with sanctimonious reverence, and deem them like the ark of the covenant, too sacred to be touched.
And there are also indented paragraphs, which begin with a tag or label at the margin and the remaining text indented.
one   This is  the first paragraph.  Notice  how the first
      line of  the resulting  paragraph lines up  with the
      other lines in the paragraph.
longlabel
      This  paragraph   had  a  long   label.   The  first
      character of text on the first line does not line up
      with  the  text  on  second  and  subsequent  lines,
      although they line up with each other.
A variation of this is a bulleted list.
.     Bulleted lists start with a bullet.   It is possible
      to use other glyphs instead of the bullet.  In nroff
      mode using the ASCII character set for output, a dot
      is used instead of a real bullet.