arara is a TeX automation tool based on rules and directives. It gives you subsidies to enhance your TeX experience. The tool is an effort to provide a concise way to automate the daily TeX workflow for users and also package writers. Users might write their own rules when the provided ones do not suffice. Now when you run arara my-file, that directive (% arara: ...) will be seen and carried out as described by the pdflatex rule. You can read more about rules and directives in the user manual. In addition to documenting all of the rules that come standard with arara, its manual gives a detailed explanation of how arara works, how to create and use your own rules, and how to integrate the tool into the common TeX IDEs.