Get vaccinated, it will make everything a lot easier. If you're not vaccinated, then you'll have to present a negative test result before entering Germany (I assume this would be done before boarding the plane in the UK), and then you'll have to go into quarantine for a minimum 5 days on arrival, after which you can end the quarantine early after taking yet another corona test. Rules vary from place to place, but many brothels/clubs will also require you to present a vaccination certificate or negative test result before allowing you in, and also some restaurants/bars/events, depending on the local incidence rate. If you're vaccinated (or you have "proof of recovery" from an early COVID infection), you can completely skip the testing and quarantine requirements.
When going back to the UK, you'll also have to present a negative test result before boarding the plane. This is a requirement of the UK government, not the Germans, and applies to everybody whether vaccinated or not. A quick antigen test ("Schnelltest") is acceptable, as long as the results are in English. Technically you have to pay if you're not a resident in Germany, but I took a test today, and they didn't even ask. The test centres get paid for each test performed on German citizens by the government, but it's not enforced very strictly, so some places may not give a fuck and test anybody for free. So you might get lucky, but you should be prepared to pay for it, probably around €20 or so.
The rules for entering Germany can be found at the following link (also in English). You should check this before travelling because they can change depending on the current situation.
External Link/Members Only