Your canvas (the white space between the nodes) really is the starting point of your flow. Here you have the option to give your flow a title and to set some defaults that may be useful for your design.
Service Name: Is your flow triggered by a Service? Infor provides standard triggers based upon transaction events. You release a requisition, IPA creates a Workunit for processing the approvals. The function that moves your requisition into the approval flow is the Service.
Click the drop down arrow and the full listing of available Services is presented to you. Is this a requirement? No, but there is a benefit. By selecting a Service, the variables that are automatically passed into the Workunit are available to you within the flow.
That means you don't have to create and assign a Company variable if the Service already passes one into your Workunit. And since these are treated the same way as the variables you define on the Start node (more on that later), these Service Variables are available to you all the way through the flow.
If the Service is updated with additional variables (or they don't show at first after selecting the Service) you can click the Reload Service variables button to refresh them.