Why am I getting ERROR: column "GLOBE-BE-154" does not exist
As documented in the manual string constants need to be enclosed in single quotes in SQL
INSERT INTO stunden_Plan (stunde, montag, dienstag, mittwoch, donnerstag, freitag)
VALUES (2, 'GLOBE-BE-154', 'CH-SCH-156', 'D-KR-477', 'M-HA-477', 'E-ZE-477' );

Double quotes are for identifiers