This is the code:
\section{Introduction}
\subsection{Background of the Project}
\setlength{\parindent}{10ex}
An Information System (IS) is a collection of integrated modules that collect, manipulate, and...
This is the output:
The \parindent doesn't seem to be working. I need the paragraph to be indented.
I'd prefer a global solution, where all paragraphs are indented unless otherwise instructed.

parindentis likely already set to a useful value; you don't need to set it again. The first paragraph after a heading (like the subsection above) is not intended by default, because that is the standard typographic convention in the English world. You can use the packageindentfirstto override this. See questions 1, 2, 3, 4, etc. – ShreevatsaR Sep 07 '17 at 02:43\documentclassand ending with\end{document}. – ShreevatsaR Sep 07 '17 at 02:44