I want to design my artwork in a size which can be fit on standard A4 paper, which means i want to print it on A4 size paper both side. I design my artwork in Adobe Photoshop. Can anybody please tell me for that what exact size I will have to work on, so that i can give it to the printing guys? I am so confused about which size i have to prepare so that i can print it on A4 size.
Photoshop already has all the settings stored in its presets to create an A4 document for you automatically, that can then be printed.
Click File > New, and choose the "Print" presets from the bar along the top, and select the "A4" blank document preset. The rest of the settings will be automatically applied to your document. Then hit "Create".
Example of the New Document dialog in Photoshop CC.
If you have an older version of Photoshop, it too will also have an A4 300ppi preset available when you click File > New. I don't have a copy of an older version to show you a screenshot.