Finally, I figured it out with the help of this answer.
The complete steps to configure arara in TeXstudio on Windows are as follows:
Download and install arara source file from Github
If you let arara be installed in the default directory (i.e. C:\Program Files (x86)\arara), create arara configuration file araraconfig.yaml in the same directory and edit it to make search path
config
paths:
C:\Program Files (x86)\arara\rules
In Texstudio > Options > Configure Texstudio > Build > User Commands, add the following command
user0:Arara "C:\Program Files (x86)\arara\arara.exe" -v -l %

Test arara by running the user command Arara you have just created on the following sample file
% arara: pdflatex
\documentclass{article}
\begin{document}
Hello, world!
\end{document}
then you will get SUCCESS in the Messages window and an output PDF file.
Needless to say, the directory C:\Program Files (x86)\arara should be changed in the previous steps according to the actual one arara installed in.
Update 1
I tried to run arara after installing it in MiKTeX package manager, but I didn't know how to make it working. So far, the first approach seems to be working and straightforward.
Update 2
Because I have been notified in the comments that this configuration file is not a valid one, I tried to completely remove this config. file and run arara again. It works flawlessly without any warning of missing configuration file. At the first run, it seems that the arara was looking for a configuration file in its installation directory regardless its content.
I completely removed arara installation directory (since uninstaller.jar has no effect) and reinstalled it again without any creation of configuration file, and it works again without any problems.
Maybe, there is some weird thing happened after I created that invalid configuration file (at the very first run) that made everything works normally from then onwards.
arara? Usually, it isararaunless it is specially capitalised for Windows. Are you using MikTeX? It is very strange if that answer is right as it would break Arara for every MikTeX user. Possible, of course. – cfr Jun 08 '16 at 00:30arara, I just want to use latexindent, and after some research, I found thatararacan provide an easy way to do so. So, basically, this is my first time to come acrossarara. For your question, yes, I use MikTex, but I don't know know how to testarara.exethrough command window. I am so sorry for lacking this info. – Diaa Jun 08 '16 at 00:34arara <filename>orarara <filename.tex.ararais the command installed by TeX Live in my case. As I say, I'm just not familiar with the terminology. On the systems I use, something is a command or not. – cfr Jun 08 '16 at 00:59araraconfiguration file wasn't provided in the first place with the default installation files. – Diaa Jun 08 '16 at 19:38ararainstallation package itself, since even when I downloaded theararainstallation file from its own website, I found this weird drawback of lacking its own configuration file. – Diaa Jun 08 '16 at 22:33ararainto MiKTeX, so the only way is through either a manual deployment or the graphical installer. I will try to contact the MiKTeX team when version 4.0 is ready, so MiKTeX users will also get updates. Regarding your question, I am a bit puzzled, asararadoes not require a configuration file to exist at all; the error being reported is about a malformed existing configuration file located in your home directory (in Windows, it'sC:\Users\Paulo, for example). – Paulo Cereda Jul 30 '16 at 13:19arara cannot proceed until a proper configuration file is provided, may I suggest modifying it so that it does not suggest that a configuration file is required? Something likearara cannot proceed with the current file. Either remove the malformed configuration file completely (to run with default settings) or correct it (to use custom settings)? – cfr Jul 30 '16 at 22:41:)– Paulo Cereda Jul 31 '16 at 10:48