Some packages have to be included in the preamble to support it, as shown below.
\documentclass[a4paper,10pt]{article}
%In the preamble section include the arabtex and utf8 packages
\usepackage{arabtex}
\usepackage{utf8}
\begin{document}
%start encoding to unicode
%Note that your layout must support arabic text when compiling
\setcode{utf8}
%To start typing in Arabic use the command arabtext
hello
\begin{arabtext}
السَلامُ عَليكم ورَحمةُ الله وبَركاته
\end{arabtext}
arabic
\end{document}
Comments
This topic was really interesting to me because I used Arabic script a lot during my bachelor's and master's degree in medieval/classical arabic linguistics and literature. I always used MS Word or similar programs to write documents in arabic, but never thought about taking LaTex for it. I tried this out and it worked well.