Skill Fields are the groups of skills the Stage 3 schools give you. The fields you can choose with each school are on pages 72-73 of AToW, and the fields themselves are listed on pages 82-85. As explained on pages 70-71, when you select a Skill Field, you receive 30 points in each skill listed as part of that field AND a 6-point rebate that you can spend on other things. Basically, you're only paying 24 points for 30 points in each skill due to the efficiencies of mass education. If you like, I can walk you through a detailed example, but probably not until tomorrow night after work.