Creating Flow Controls 
In this step you create flow controls to connect flow objects and artifacts with them to model a finished structure of a business process model. The flow control types used in the current business process model are sequence flow and data flow connections. Sequence flow connections define the order of performance of flow objects. Data flow connections define where data objects are used in your business process model.
Procedure
Creating Sequence Flow Connections
From Palette, expand Connections.
Choose Sequence Flow and choose Book order request start event.
Create a connection to Availability check automated activity using drag and drop.
Connect Availability check automated activity to Book availability exclusive choice. To do that, repeat the above steps.
Choose Book availability exclusive choice and create conditional sequence flows in the following way:
Book is available: Create a conditional sequence flow connection (a sequence flow connection starting from a gateway) to Book delivery human activity using drag and drop.
In the context menu of the conditional sequence flow connection, choose Default Gate to make it the default alternative.
Assign a name to the connection. To do that, choose General in the Properties view.
Enter Book available in the Name field and optionally a description in the Documentation field.
Book is not available: Create a conditional sequence flow connection to Book replenishment human activity using drag and drop.
Assign a name to the conditional alternative. To do that, choose General in the Properties view.
Enter Book not available in the Name field and optionally a description in the Documentation field.
Connect the Book replenishment human activity to the Book delivery human activity using the above steps.
Connect the Book delivery human activity to Delivery receipt end event. To do that, repeat the steps above.
Creating Data Flow Connections
From Palette, expand Connections.
Choose Data Flow and choose the Book order request start event.
Create a connection to the Book_order_details data object using drag and drop.
Choose the Book_order_details data object and create a connection to Availability check automated activity using drag and drop.
Connect the Availability check automated activity to the Customer_details_form data object and then the Customer_details_form data object to the Book delivery human activity.
Connect the Availability check automated activity to the Book_replenishment_form data object and then the Book_replenishment_form data object to the Book replenishment human activity.
Result
Your have connected all your flow objects and artifacts to model the outline of a business process model.