Line Spacing Options

Question

How can I add space before and after a paragraph, and how do I adjust it?

Here is the code, how could I adjust the line spacing in it?

\documentclass[11pt,a4paper,twoside,openright]{report}
\usepackage{soul}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
%\usepackage[portuges]{babel}
\usepackage{fancyvrb}
\usepackage{multirow}
\usepackage{graphicx}
\usepackage{svg}
\usepackage{subcaption}
\usepackage{enumitem}
\usepackage{tabularx} 
\usepackage{booktabs}
% \setlist{nolistsep,leftmargin=*}
\setlist{nolistsep}
\usepackage{ragged2e} 
%\usepackage{epstopdf}
\usepackage{rotating}
\usepackage{slashbox,pict2e}
\usepackage{amssymb}
\usepackage{lscape}
\usepackage{longtable}
\usepackage{makeidx}
\usepackage{amsmath}
\usepackage{multirow}
\usepackage{makecell}
\usepackage{wrapfig}

\usepackage[utf8]{inputenc}
\let\cleardoublepage=\clearpage


\StartBody

%% TIP: use a separate  file for each
\include{chapter1} 
\appendix
\include{appendix1}

\begin{singlespace}
  \PrintBib{references}
  \PrintIndex
\end{singlespace}

\end{document}

%Chapter 1

\chapter{Chapter 1 title} \label{chap:concl}
%\version{v1.10.2015}
\section*{}
\lipsum
% Line Spacing
\section{Sec}
\lipsum

Answer 1

1. The normal space between paragraphs is set with \parskip, that could be a moderately stretchable and shrinkable glue to fit better the text to the top/bottom margins. Beside that, the package parskip set the paragraph skip by default to 6 pt (stretchable to up to 8pt when needed) and some other things (read the package manual, it is short).

   \documentclass{article} \usepackage{lipsum}

   %\usepackage{parskip}

   \begin{document}

   Spaces of \the\parskip:

   \lipsum[1][1-4]

   \lipsum[2][1-4]

   \setlength{\parskip}{20pt plus 4pt minus 4pt}

   Spacing of \the\parskip:

   \lipsum[3][1-4]

   \lipsum[4][1-4]

   \end{document}

2. The interline space within paragraphs is a different hairy beast, and it can be set in different ways. See here to understand what I mean.