if I already have a height and width of 1920 1080 then what is the setting that says Resolution "72" used for? I have not used adobe-photoshop in forever and I am just getting back into it. so sorry if this has been asked before. see picture below to explain what I am trying to ask.
It tells how to convert your artwork to physical units. So essentially its how many pixels form an inch. If you design for print you should set it to 150-300 and type physical dimensions of your output (not pixels). If not leave it as 72.
For historical reasons 72 means value not set, which in turn means designed for a screen device. (Why 72? Adobes internal unit is a postscript point so 72 pixels per inch means one internal unit equals to one pixel which is nice if the unit is meaningless for you)