Other Variables are just normal variables which you might create in a Command Sequence using a Command like CreateVar, except they can be created from within the Start node to save unecessary Commands at the start of a Command Sequence. They must have a value (as well as a name) assigned to them when they are created.

Other Variables can be added by selecting the start node in a Command Sequence, going to the 'Other' tab in the properties panel and adding the other variable name and a value to the list.