The tutorial documents the overall structure of a SOD recipe. You should read through it if you are unfamiliar with how a SOD recipe is formed.
The ingredient listing contains a page for every ingredient that can go into SOD. If you want to extend and improve your SOD runs, it's the place to find pieces of SOD that do what you want.
An ingredient is a single operation in a recipe. A full SOD recipe consists of multiple ingredents that tell SOD how to gather and process data.
Each ingredient's page consists of four major sections: a description of the ingredient's uses, an example of the ingredient, an abstract description of the ingredient's structure, and a list of all of the ingredients that contain this ingredient.
The example of the ingredient. You can copy the example, paste it in the correct place in a recipe, and SOD will start using it.
This section describes the exact structure of the ingredient. It's important enough to get its own page explaining it here.
This section lists every ingredient that contains this ingredient. In the case where this is contained in a choice, the items that can be substituted for this are listed as well.