The underscore character ‘_’ is ordinarily used in
TeX to indicate a subscript in maths mode; if you type
_, on its own, in the course of ordinary text, TeX will
complain. If you’re writing a document which will contain a large
number of underscore characters, the prospect of typing
\_ (or, worse, \textunderscore) for every one of
them will daunt most ordinary people.
Moderately skilled macro programmers can readily generate a quick hack
to permit typing ‘_’ to mean ‘text underscore’.
However, the code is somewhat tricky, and more importantly
there are significant points where it’s easy to get it wrong. There
is therefore a package underscore which provides a general
solution to this requirement.
There is a problem, though: OT1 text fonts don’t contain an
underscore character, unless they’re in the typewriter version of the
encoding (used by fixed-width fonts such as cmtt). So either
you must ensure that your underscore characters only occur in text set
in a typewriter font, or you must use a more modern encoding, such as
T1, which has the same layout for every font, and thus an
underscore in every font.
If the requirement is only for occasional uses of underscores, it may be acceptable to use the following construct:
\def\us{\char`\_}
...
\texttt{create\us process}
The construction isn’t in the least robust (in the normal English sense of the word), but it is robust under expansion (i.e., the LaTeX sense of the word); so use it with care, but don’t worry about section headings and the like.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=underscore