Based on your consumption estimation, your electricity provider will calculate a monthly prepayment rate. This prepayment rate will be
either deducted from your bank account, if you agreed to direct debit (Lastschrift)
or you will need to transfer it yourself every month.
After a year (usually), they measure your actual consumption.
If you used less than your estimation, you will get money back and your monthly prepayment rate will be lowered.
If you used more than your estimation, you will need to pay the difference and your monthly prepayment rate will be raised.