This sectoin of the economy produces raw materials such as food crop, timber or minerals. Occupations in fishing , farming, forestry and mining are all examples of primary economic activities.
The secondary sector is involved in processing and manufacturing. Food processing, the textiles and clothing industries and manufacture of microchips are all examples of secondary occupation.
This section provides services to other industries or to individual consumers like you and me. Employment in a school, shop, office are all examples of that answer and tertiary occupation.