Variables can be used to pass parameters between actions. When a variable value is changed the VariableChanged event is executed. The variable values can be saved with WorkflowAction=>SaveVariables this values are loaded automatically except variables which are set the Reinit after session which will be initialized with the default values. In runtime the values of a variable can be changed using view elements (like text or browse) or using Assign action. In action the variables can be used with {} except condition fields and assign formula.
For this variables values are assigned automatically, but required to be defined.