Can you buy beer in Germany?
To work legally you need a tax number.
Register your address with the local authority. Get a residence permit if you are a non EU Citizen. Get a tax number.
That all happens at the local authority.
Get your first emloyer to get you a social security number.
Unless you are working cash in hand (of course that NEVER happens in Germany with young immigrants in the first jobs

) you will need a bank account.
There are varĂous commercial and public banks out there who you could give your business to; each has its advantages and disadvantages.