Once you have identified the operation, go back to vRO. Enter the resource URI. This includes the root object and any parameters, filters, or sorts. The workflow automatically adds the FlashArray address and REST version.
So if you want to pull all volumes from a FlashArray you would enter /volume (don't forget the preceding forward slash) and choose GET and click Submit (note that this is a default workflow--use that instead of doing it here, using this though as a simple example).
If you want to pull the space stats of a volume named activeDRpodA::ActiveDRVMFS-01 and with a query parameter of ?space=true