Hi
abalfazl,
Welcome to WebProWorld!
So you're starting with the 'easy stuff' for your first post are you? :o)
EasyWebDev gave an indication on how to get started with your own
PHP Webmail service.
All of this presumes you have administrative access to a web server. You will also need to set up an email server before you can start installing any webmail software.
There are three popular email programs generally found on most Apache hosted setups,
NeoMail,
Horde and SquirrelMail.
Installing SquirrelMail
Paul