The Begin Step is where all charts start, and cannot be removed, cut, or copied. The begin step is where you can define initial values for your chart's scope. These initial values are also hints as to what parameters your chart expects. If the chart receives any of these parameters as starting parameters, the initial values are ignored.
One of the chart parameters defined on the begin step can be marked as the Key Param. This means that this parameter is used as an identifier for the chart. For example, suppose your chart defined the automation process for a car through an assembly line. You can define the car's VIN as the key param, which means that instances of this chart are identified by the VIN they were started with.