What is the main purpose of a Realschule in Germany?
A Realschule accommodates children who do not expect to go to
university (there's a "Gymnasium" for that; from which the final
exam (after year 12 or 13, depending on which state you're in)) is
called the Abitur (like the French Baccalaureat and the equivalent
of Enlgish A' levels).
It is possible to get a Mittlerer Reife' qualification from the
Realschule (after year 10).
With this it should be possible to get a reasonable office job,
or attend a "Fachoberschule" for another two years to get the
Abitur.