The task flow contains three view activities: welcome, products and stock, and three control flow cases. The first activity you dropped is the default, as indicated by the green halo or circle. Currently the task flow does not do anything: the ! icon on each view activity indicates that the view activity is not bound to any page. Later you will tie a page to each view activity, and add navigation.
You can see the rules that JDeveloper has added to the task flow file using a visual format by clicking the Overview tab at the bottom of the editor window and selecting the Control Flows navigation tab at the left, for example:
You can see the same rules in the XML source of the task flow file by clicking the Source tab at the bottom:
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