Firstly, Thanks for the support by Caramdir.
After playing there are two ways for adding different search path directories:
1- goto options -> execution modes -> variables
2- check on the TEXINPUTS then type in its field (e.g. in case of adding "C:\Texproject"):
- "C:\Texproject" for adding only this directory
- "C:\Texproject//" for adding this directory and its subdirectories
1- goto options -> execution modes -> PATH
2- For the first option "EXTRA PATH FOLDERS", check on "Insert in PATH" then click on the magnifying glass for browsing to any folder you want to add.
3- Select the folder, then click open twice.
The second method only add this directory without its subdirectories.
For the two methods, adding multiple directories is possible by separating each two paths by semicolon.
Waiting for any amendments.