How to create A New Document in Adobe Photoshop

All of the software has the 'New' option in "File" menu. Adobe Photoshop too like that. 
fist you go  to "New" on "File" menu

When you click on "New", It will appear a dialog box. There are many options for you about a new document you ware created. Following options have been filled by you

1. Name: This is the name of your new document. it will appear on top of your document Title bar.
2. Preset: There are lot of presets has been created by Adobe company. such us

• Default Photoshop size (7 inch x 5 inch, resolution 72 pixels/inch)
• US Paper size (Letter,grant format,Tabloid)
• International paper (A3, A4,A5,B3,B4,B5....)
• Portrait 2 x 3 inch, 4 x 6 inch, 5 x 7, 8x10
• Web (640 x 480 pixel , 800 x 600 px, 1024 x 768 px, .....
• Mobile and Devises (176 x 208 px, 176 x 270 px, etc. ) 
• Film & Video 
• 

You can select from above one of the size for your work. when you select the size you have to select your colour mode too. Normally RGB colour code is using all work, But some times you have to changed it as CMYK when you using Four-colour Technology printer.

After you have to decide which background colour will appear when you start your work. There are Three option for you 

1. White 

2.Background colour 

3.Transparent 

No need any pre-setup when you select White or Transparent but you must select your own colour before you select Background colour from "Tools" window. Screen shot is below 

F - Foregroundcolour 

B- Background

Now you finished 90% of your work. Finally you can save as preset of your custom setting. It will help when you use again this same setting.