The scythe is the most versatile resource harvester of the game. You can get randomized items and grass is abundant.
Scythes are made with 1 - 5 wood, depending on the number of minions in your tribe. You need to select scythe from improvement icons first. After that, to give one to your minions, select it on the left, and then click any available minion to make them a farmer. Scythe is a melee tool, so it can be paired with shields.
When you research scythe, you also two other abilities appear in the improvements bar: farming and mycology.
Farmer minions will automatically move to chop grasses when they are in range of one. They will slice the grass and then a random resource will appear.
In battles, farmers move to attack any opponent that isn't already engaged by another minions. Like in all fights, knight minions are attacked first and hunter minions are attacked last.
Tips and Tricks
This is the best improvement to gather resources because grasses are easy to find and will yield any resource. The two skills it unlocks are both used to get food, so if you find yourself low on food, you might want to consider using scythe.
On the other hand, it might not be worth it to waste upgrades on scythe, mycology, or farming when you can easily get food other ways, like trading gold for it, fighting, or simply memorizing the mushrooms.
In Castle Mode, corn can be planted for the price of one food, and later harvested for two. However, having multiple farmers swing at one corn crop at the same time will yield twice the amount of food as there are farmers swinging at it.