Set Line Space in LaTeX

The parskip command makes a skip between paragraphs. The length of skip can be set using the command \setlength, e.g.,
```
 \setlength{\parskip}{15pt plus 1pt minus 1pt}
```
The command \itemsep sets the space between items in lists, e.g.,
```
 \begin{itemize}
 \itemsep = 0.8cm
 \item 
 \end{itemize}
```
The command \doublespace makes lines after this command double spaced. This is convenient to produce PDF document for review.