In LATEX, there are two parameters influencing paragraph layout.
By placing a definition like
in the preamble of the input file, you can change the layout of
paragraphs. These two commands increase the space between two paragraphs
while setting the paragraph indent to zero.
The plus and minus parts of the length above tell TEX that it can compress and expand the inter paragraph skip by the amount specified, if this is necessary to properly fit the paragraphs onto the page.
In continental Europe,
paragraphs are often separated by some space and not indented. But
beware, this also has its effect on the table of contents. Its lines
get spaced more loosely now as well. To avoid this, you might want to
move the two commands from the preamble into your document to some
place below the command \tableofcontents or to not use them at all,
because you'll find that most professional books use indenting and not
spacing to separate paragraphs.
If you want to indent a paragraph that is not indented, you can use
at the beginning of the paragraph.6.2 Obviously,
this will only have an effect when \parindent is not set to
zero.
To create a non-indented paragraph, you can use
as the first command of the paragraph. This might come in handy when
you start a document with body text and not with a sectioning command.