There is currently a 4.95€ fee for registering with emmy. You also get 15 free minutes with your registration (valid for 3 months).
The rides will be billed according to an unlock fee and minutes spend on an emmy . So you only pay for emmy if you use emmy. One minute of riding starts at 0.33 € and one minute in parking mode costs 0.19 €. You can find more information here: Prices.