When we need to develop (Design site )the other web site are we need enter to source code of this site or what for develop for this site ?

depends on the framework your website is based on, 

Yes you can design your site in Photoshop but one thing you have to code after designing to show perfect on browser that is a must. i mean you can design website on many softwares that you are comfortable with because there are lots of software on internet which allows you to design websites even there are some softwares available which allow you to design and the backend code automatically generat for you.its mean you do not have to code your design. For best practice and result design it in photoshop and then use your html,css skill code it.

thanx but  I mean that he Is it possible to use special software to design 

Or by Standard Code.