You build a flowchart by setting the ShapeConnectorType on the first shape to Flowchart.
By default, shapes will be added to the right of the first shape and the line connecting them will have an arrow pointing from left to right.
The defaults can be overridden.
The biggest difference between a flowchart and tree style diagrams is that with a flowchart you can define multiple ShapeConnectors. This allows you to add shapes in different directions. One path leading to the right of the first shape and another downward.
If you add multiple ShapeConnectors going in the same direction, you'll create a split path.
Learn more about creating flowcharts:
Learn more about ShapeConnectors: