difficulty with trading section

hi

i am a newcomer to the game and have got the hand of it quite easily however i have one topic i struggle with, that being the section of agriculter, industry, services, trade. i never bother with it because i am confussed with what i am supposed to do with it, but i get messages sometimes saying it doesnt look good and i shouold do something about it.

could anyone offer any hints and tips or a tutorial in this section

thanks
(PS sorry if this is under the wrong topic not sure were to as this question)