Utilities are the links to important elements of the site that aren’t really part of the content hierarchy. These are things that either can help me use the site (like Help, a Site Map, or a Shopping Cart) or can provide information about its publisher (like About Us and Contact Us).
Don’t make me think
Being an expert in online usability Krug gathered his experience in a wonderful book. This summary of key thoughts will help you to remember most important principles and laws.