Hi. I`m pretty new to Blue Prism myself, so bear with me if I don`t quite understand your question.
Nevertheless, in Process Studio you lay out your process, and whenever the process needs to interact with another system, Business Objects are used to interact with those.
In addition, Business Objects provided by Blue Prism deliver common methods that most of us find useful, like interacting with Excel, E-mail etc.
You also use Business Objects when interacting with queues in Blue Prism. Furthermore, it is possible to extend functionality by creating your own libraries (assemblies/dll`s if you like) and hook up to those via a Business Object.
Regards, Jardar