Windows Services are non-UI software applications that run in the background of your Windows operating system. They are continuously running applications doing all the heavy lifting without being noticed. JudoManager.Service (usually referred to as the Service) is one such service.
The Service connects various modules together. It is responsible for sending and receiving data from one module to another. For example, the Accreditation module needs the Service to be running to be able to connect to JudoManager Desktop application and use the registrations data already available there. It works both ways, without the Service, JudoManager Desktop application can not synchronize with changes made in the Accreditation module. Same goes with all the other modules.
So, in short, if you wish to work with multiple modules, make sure that the Service is running!