The Default currency. is the currency which you will use the most. You can define this currency in the settings on the Working environment tab in the Desktop Client. This sets the default currency if a drop-down list is available for selecting a currency.
The Base currency is the currency which is used in your company and it should already be set in the currency selection drop-down list, if you have not already set a default currency.
Your administrator defines the following options in the Management Console: