A job is any legal activity that allows an individual to perform a service and in return earn credits she/he can use to buy things.
A job can mean "some work that has to be done", for example: there are jobs to be done in the house: washing up, mending things that are broken, etc.
A job can also mean: work that a person does to earn money. The word "job" may be used when a person works for someone else "an employer" who pays them for the work. For example, a teacher's job is to teach children or adults. A taxi driver's job is to drive people in a taxi. A firefighter rescues people from burning buildings and puts out fires. A dermatologist's job is to diagnose and treat skin diseases. Some jobs pay very little.
The International Labour Organization was established to make people's job conditions better. It became an organization of the United Nations in 1946.