Answer:
on the job training.
Step-by-step explanation:
This is a modern version of an apprentice learning how to work from a master craftsman.
Before when Universities or technical colleges didn't exist, experienced craftsmen had apprentices that helped them do their work and at the same time learned how to perform the tasks.
The modern version, called on the job training, is a similar hands on learning method where an experienced employee teaches new employees the skills, knowledge, and competencies that are required to perform certain tasks correctly.