Simply place the chain around a fixed object, pull the end with the lock through the ring on the chain, and attach it to the lock housing. You will not need another key, nor will you need to lock the shackle separately.
The ABUS Adaptor Chain requires the RadCity Wheel Lock by ABUS, which is only compatible with RadCity and RadMission ebikes.
Want a longer chain to secure your front wheel as well? Check out the 130 cm length by ABUS.