Ahoi Quisi!
To get a networkwork connection with your iPad in a mobile network, your iPad needs a SIM card. Otherwise you are restricted to the availability of WLAN.
If you got a SIM card of your provider of your country, you will be able to get a connection in Germany but you will have to pay for the roaming, which normally is very expensive.
So it is a good idea to get a SIM card of a local provider.
There are 2 ways to get this card.
1. Contract, you pay monthly a certain amount and get connection. The prize varies in speed and amount of data
2. Pre paid: you buy a SIM with a certain amount of data volume, e.g. 5 GB, when it's finished, you have to buy a new amount.
Number is preferred when you only stay a few days in a foreign country.
Number 1 is preferred when you stay longer as the contracts usually last for a couple of month or 1 or 2 years
Greetings