Variables are used to handle the state of various workflow related information that doesn't justify a state of it's own. The default CMF workflows use variables to track status history comments, and store the the last transition, who initiated it and when, for example. From the variables tab it's possible to add new variables, and rename and delete existing variables.
The list of existing variables also displays a summary of each variable's description, catalog availability, workflow status, default value or expression and any access guards. You can click through to each variable to configure it's details.
In each variable's property tab you can set the variable's description and a collection of properties the define the variable's behaviour, as follows:
State variable - stores the name of the variable the current state of
the content is stored in. CMF uses
review_state by default, and will
have already created a FieldIndex for it. The state variable is
effectively a variable with "Make available to catalog" set, a default
value of whatever the initial state is and a default expression that
sets to the new state on every transition.