Function Modules Description
SWU_START_WORKFLOW To start Workflow
SWE_EVENT_CREATE To create Event
SWW_WI_DISABLE For locking of work items against execution
SWW_WI_ENABLE For enabling of work items against execution
SWW_WI_CONTAINER_READ To read the container elements of a particular work item
SWW_WI_DEADLINES_CHANGE To change the attributes of the deadline monitoring for a particular work item
SAP_WAPI_EXECUTE_WORKITEM To execute workitem of another user
Other Useul Link :
Important Transaction in Workflow
Workflow Benefits for the company
Introduction to SAP Workflow
Workflow ?
Org units in workflow steps?
Workflow performance tips