A tutorial on how to use the Ada 2012 features for specifying detailed, checked contracts for types and subprograms -- "classes, functions, and methods" if you aren't an Ada programmer already. Contracts document constraints on how types and subprograms behave, but unlike comments they are checked -- either by when the program is compiled or on-the-fly as the program is running. Ada 2012 contract aspects will be presented together with a set of guidelines for using contract aspects consistently. The tutorial will conclude with a live test of the guidelines on some example source text.