It can be accessed via the settings menu.
Configured workflows are standard Pimcore Workflow Engine workflows. They appear alongside other configured workflows in the system on the Pimcore elements and the Pimcore Workflow documentation applies in terms of features, behavior and configuration options.
To apply workflow changes to Pimcore, the symfony container needs to be rebuilt. On development systems (in dev environment) this might happen automatically just when saving the workflow definition.
On production systems (in prod environment) it might be necessary to choose the
Save and Rebuild option of the save button.
This issues a symfony container rebuild to apply all the workflow definition changes to Pimcore.