Cross-stage workflows for beginners. Part I. SharePoint Designer

Hello!
One of the most important things in SharePoint 2013 is cross-stage workflows. SharePoint 2010 has "sequential" chain-like workflows with plain passage in flow. Sequential workflows pass through the flow from start point to end point with executing a defined set of activities. This is restricting your vision of any workflow in your organization. Let me show you how you can implement workflow with a complex business logic.