Local Variables: identified by a unique name. Only affect one scene.
List Variables: An array of values accessed by index. Only affect one scene.
Variables can also be accessed through code. Head to Variables Access to know more.
Anatomy of a Variable
A variable is has a name that identifies it (for example: “shotgun ammo“) and a value.
A variable can have different types of values, including character strings, numbers, booleans (on/off), Colors, Vector3, and references to GameObjects.
Next to the name there's a checkbox. This allows to save the variable's state between play sessions
Not all variable types allow to save its state. For example, Game Objects can't be saved because they are a reference type, which Unity doesn't allow to serialize.