Currencies are and Enumeration Type. They are generic values that can be counted. All Currencies can be used in Resources or Conditions that use a Wallet. For example, you might create a Currency called “dollars”. In a Script, you can give a user a Reward for completing a Task. Part of that Reward might be giving the user five dollars. At a later point in your Script, you can create a Precondition which requires the user to have five or more dollars to progress.
The name Currencies can be misleading. You can also make a Currency called “Experience Points”. It is simply a value which can be incremented or decremented. If you ever need to keep track of how many times something has happened to a user or the quantity of something that the user has, a Currency is a good option.