When you create your new document you specify a range of colour settings plus page dimensions depending on the purpose of your document.
Available new document settings are as follows:
Type—Select the aim and deliverable for your project (for quickly populating settings below). As well as print (press-ready CMYK), you can work to specific Photo print sizes, specific Web screen resolutions, and with the Devices option, design to iPad, iPhone, and Nexus document specifications.
Page Preset—Offers sizes for UK/US print, photos, screen use, and mobile devices. A Custom option indicates if your page is using non-standard page dimensions.
Document Units—Displays your rulers and object dimensions in pixels, points or using physical measurement units.
Colour Format—Sets the colour mode to RGB or Grey (8 or 16 bit), CMYK (8 bit), or Lab (16 bit).
Colour Profile—Sets the colour gamut for the previously chosen colour format.
Transparent background—Check to set your page background to be transparent.
Page Width/Height—Change these values to make a custom page size. (An alternative to selecting a Page Preset size above.)
DPI—Sets the resolution of your document. For example, for professional print quality, set your resolution to 300 dpi.
'Actual Size' Zoom—Sets the device which is mimicked when presenting the document at 'Actual Size' (from the View menu). This option is only available when the document units are set to Pixel or Points. Select from the pop-up menu.
Portrait—Uncheck to present your document in landscape orientation.
Include Margins—Check to switch on page margins.
Left Margin, Right Margin, Top Margin, Bottom Margin— Sets the printer margins, showing as non-printable blue lines. Click Retrieve Margin from Printer to use your default printer's settings.