President John F. Kennedy’s speech at the Berlin Wall always reminds people of his famous quote: Ich bin ein Berliner! Even though he meant I am a citizen of Berlin!, he really ended up saying I am a jelly doughnut! (But the Berliners knew what he meant ‑ phew!)
The mistake was with the word ein. When talking about your nationality or profession, don’t use ein before it!
The basic form of many occupations in German refers to a man in the position, like der Chef. If your boss is a woman, however, you’ll refer to her as die Chefin!
A saying worth knowing is Übung macht den Meister! which literally means Practice creates the master.
In Germany, many people work apprenticeships to learn a trade (for example, locksmithing or carpentry!) and eventually become a Meister.