I downloaded Miktex2.9 but when I try to type Farsi(persian) it does not recognize the xepersian package and give an error instead. I need to add the xepersian or other packages to my Miktex please tell me how to do it.
Apparently you installed MikTeX basic, which does not have
xepersian included. One way to install
xepersian is using mikTeX on-the-fly package install, but not recommended. There might be dependencies you miss.
The best solution I recommend is installing Texlive 2013 and update it. Installing miktex (complete) is another solution, but you must make sure it contains latest
xetex binaries. Older versions of miktex was shipped with old
xetex binaries and caused some bugs in RTL typesetting.
Open the MiKTeX Package Manager as Administrator; you'll see he whole list of packages in MiKTeX distribution. Right click on the
xepersian package (you may type "xepersian" in the small
Name window at the top and
filter the packages list) . A small menu will popup; choose "install". That's all. Any additional package can be installed in the same way.