A short video:
Click on Create App and enter a flow name
Edit & Save:
To edit a flow, click on App Bazaar --> Installed Apps --> Edit Call App link next to the call flow that you would like to modify
You can drag and drop the required applets to create your flow. You can understand what each applet does by hovering your mouse over the applet. You can also find detailed information on each Applet and its functionality here
Once you have created a flow, you can 'Save' and 'Close' it
Having created a new flow, if you wish to test it out - please follow the steps documented here: How do I test out the new business logic that I've created?