You first need some stats to find
Wild windsown weed.
Then you need herbalist table and windsown weed will turn to random seeds after few hours (2-3 irl).
You can also just ask for some seeds when you meet people.
After you get seeds, you plow land by hand or by plow tool.. thats where seeds are planted.
Thats all.. no watering.. no compost.. you just wait some time depending on crop and voila...