Notes:

Creating a new document in Photoshop :

While designing graphics, Setting up the new document correctly is one of the most important step.

First of all we need to understand, Is the file meant for digital media or print media?

As we know that Photoshop is used to design graphics for various domains especially
digital media (like PC, mobile, tablets, web, TV, etc.),
print media (like newspapers, magazines, wall posters, books, broachers, photographs etc).

Photoshop provides some of the predefined set of common document sizes for various domains as well as it allows creating document of required size i.e. we can setup the document according to our requirement.

File Menu – New – Setup the document – OK

Name of document:
You can set any name for the new document (optional)
Presets dropdown box:
You can select predefine domain for new document
Size:
You can select a predefine size for the new document
Width:
You can set the width of the new document
Pixels for digital media and inches for print media
Height:
You can set the height of the new document
Pixels for digital media and inches for print media
Resolution:
72ppi for digital media and 300ppi for print media
ppi : pixels per inch
dpi:dots per inch
lpi: lines per inch

Color Mode:
RGB for digital media and CMYK for print media
Bit depth:
8 bpc is common and for HDR set 16 bpc or 32 bpc
bpc : bits per channel
Background content:
White, Background Color, Transparent

Color Profile:
sRGB is common, for HDR ProphotoRGB or Adobe RGB
Pixel Aspect Ratio:
Square Pixels is common. For video you can choose others.