The FlowReactorComponent runs your graph in the scene. Usually you can simply drag and drop a graph on to any game object and it will create the FlowReactorComponent automatically with the assigned graph.
Open (Open Instance)
Opens the assigned graph. At runtime, you can also open the actual running graph which is an instance of the original graph. (Open Instance)
Disable this graph
Draw node gizmos
When enabled, node gizmos will be drawn. Use the OnNodeDrawGizmos method to draw gizmos in the scene for custom nodes.
Node controlled objects
This is where you can assign components which implements the INodeControllable interface.
For more information about node controlled objects, have a look here: