Quick reference guides can take many forms. They could be terse instructions with bullet points that condense a process to one or two pages. They could be charts or even graphics. Most quick reference guides can walk the layman through a process, while others--notably the Circle of Fifths for musicians--appear to mean nothing unless you're trained to read and use them.
Most quick reference guides are designed for users who know the material or task but need something in front of them to remind them of the steps. A quick reference guide can take the form of an outline, a chart or a series of bullet points.
Quick reference guides can be professionally made or hand-written, from business card size on up. These guides may be in the form of laminated cards, index cards, punch lists, booklets or posters.
Instructions to many electronic appliances often come with a quick reference guide that shows the basic steps to get the appliance operational without the user having to wade through pages of instructions. Many operations manuals also include a troubleshooting chart--another quick reference guide that can be handy if the appliance does not work.
Computer programmers make extensive use of cheat sheets, particularly when using programs that require many keyboard commands. The console-based vi and emacs text editors, both popular for coding, use a complex array of commands to get work done.
Students know about quick reference guides. The CliffsNotes series bailed many a student out of a bad grade when he didn't have the time or inclination to read an entire book. But these are much larger than a quick reference guide. Students can buy smaller, more concise guides that boil down the key points of a class or book to a two-sided sheet.
Schooled musicians know about the Circle of Fifths, which condenses a great deal of music theory into a graphic that can be read like a clock face. Though somewhat cryptic, this graphic shows the relation of one note to another and enables musicians to understand chord progressions and scales.