Variables component allows you to add custom variables for later use.
Variables component has no unique node definition to be configured, you can give it a name and a description.
Enable/Disable port allows you to generate data only when you need it. The port value must be boolean (True or False for enable and disable respectively). By adding input ports you can forward input values as output values. Also, you can use Import/Export feature for lightweight way to add input ports.
This part allows you to choose variables from list or enter custom variables. Also, you can use Import/Export feature for lightweight way to add output ports.