(Once again, I am unsure of what a visa is. Sorry.)
Citizens are allowed to live and work in their homeland. Foreigners need permission. The details depend on the laws of the destination country, the country of origin of the applicant, and the length and purpose of stay.
- Sometimes the application must be made before arrival. This is called a visa or an ESTA. The applicant fills a form and usually she sends the passport in to have a stamp or sticker added. (The US insists that an ESTA is different from a visa, but if it quacks like a duck, it probably is a duck.)
- Sometimes the application can be made at the border on arrival. This is called a visa on arrival or some other names. There is a stamp in the passport and a time limit for the visitor to leave.
- Sometimes no stamp is necessary and no record is made, really visa-free travel. That only happens if the countries trust each other that there will be no illegal immigration or similar problems.
As a German citizen, you are a citizen of the European Union. With your parents' permission, you can travel to any of the 28 EU member states. Once you are old enough, you can live and work there. The exception would be if you, personally, get deported and banned from an EU state, but you would have to do something outrageous to make this happen.
You cannot get a visa for any EU member unless you lie about your German citizenship, because you don't need one.
You will need no passport in the EU once you have your German identity card (Personalausweis) at age 16.
The United Kingdom is about to leave the EU. It is unclear when that will happen and which rules apply afterwards, but in all likelihood you will either need a visa on arrival or no visa at all for a visit. Living and working there will require permission.
Some EU states (and some others) have formed the Schengen travel area. This actually makes little difference for you, because you have visa-free travel in those states anyway.