The initial flow is the execution starting point. The initial flow points to the state that the object, use case, or operation enters when the activity starts. You can also add a flow final to a SysML activity diagram to terminate a sequence of actions without stopping an activity.
The object flows are used to connect action nodes, activity parameters, action pins and object nodes together to define the sequence of flow of information or physical items in an activity.
To add input or output parameters to the action, see Adding Action Pins to object nodes.