Once you take a sector (it will become yours after the update), you can redesignate that sector so it produces what you want. For example, redesignating to a farm will make that sector produce food, and so on. Sector designations are described in great detail later, but you should know now that to change a designation you use the [Z]oom key to focus on the specific sector, and then you can change the designation with the [r]edesignate key inside the [Z]oom screen. You will be given a menu of possible designations.
To help you choose a designation for the sectors you take, the sector window (to the bottom right of your screen) shows you the soil, metal, jewels in that sector. If the soil value is high, then redesignating to a farm is a good idea. If the sector has a high metal yield, you might want to make a metal mine out of it, and so on.
Below is an example of a sector window that shows a sector with jewels 5, metal 0 and soil 6. The sector belongs to nation Khazad Dum, has coordinates (2, 2) relative to the current player, has 452 inhabitants which are of race (D) (Dwarves).
Hmm: think about putting it on the same page or a new page
+----------------------+ |(2,2) | |Khazad Dum-jwl. mine | |Brush Plateau | |452 people (D) | |metal 0 jewels 5 | | soil 6 movecost 1 | +----------------------+