I give it a try:
Standard Behaviour
The standard paragraph shows an indentation in the first line and no space between paragraphs (\parskip is zero).
\documentclass{article}
\usepackage{blindtext}
\begin{document}
\blindtext
\blindtext
\end{document}

Standard Document Class Solution
You can use the parskip package (CTAN link) to solve your problem.
From the documentation:
Package to be used with any document class at any size. It produces
the following Paragraph Layout:
Zero Parindent and non-zero Parskip.
The stretchable glue in \parskip helps LaTeX in finding the best place
for page breaks.
In addition, the package adjusts the skips between
list items.
This package is no more than quick fix; the ‘proper’ way to achieve
effects as far-reaching as this is to create a new class. An example
class is to be found in the ntgclass set: artikel3.cls
The koma-script bundle classes and the memoir class all provide
similar functionality, and their respective documentation files
discuss the pros (such as they are) and cons of this approach.
\documentclass{article}
% new package
\usepackage{parskip}
\usepackage{blindtext}
\begin{document}
\blindtext
\blindtext
\blindlist{itemize}
\end{document}

Bad Solution: Manually Change the Lengths
Important for you is that the package parskip takes care of other things too. Sometimes you see people manually changing the parameters like \setlength{\parindent}{0em} and \setlength{\parskip}{1em} but this is considered bad because it also could change the distance between items in lists and so on. But I am not an expert here.
Alternative Solution: KOMA Approach
There are the so called KOMA-Script (CTAN link) document classes (in contrast to the standard document classes like article and book).
They offer a document class option called parskip which also "takes care of everything".
\documentclass[parskip]{scrartcl}
\usepackage{blindtext}
\begin{document}
\blindtext
\blindtext
\blindlist{itemize}
\end{document}

PS: I don't get the
\section*{\hspace{150pt} Motivation}
\hspace{10pt}\begin{normalsize}
part of your code.
\begin{normalsize}is wrong in the sense that\normalsizeis a font size switch, but no environment. Normally, a paragraph directly after a section heading isn't indented. Use\section*{\centering Motivation}\leavevmodeand an empty line, remove\hspace{...}and then continue withtagging– Dec 29 '15 at 07:52\hspace{10pt}if you don't want the paragraph to be indented by10pt. And, get rid of the redundant and ill-formed instruction\begin{normalsize}. – Mico Dec 29 '15 at 08:18