Who generates demand, supply in the labor market? What is special?

The supply on the labor market is formed by employees, demand – by employers.
People by necessity are able to master new professions for themselves, to move because of work, etc.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.