History of Plows
If you are going to plant seeds, like wheat seeds for example, and harvest them, then you are going to have to plow. Plowing is the hardest work of farming. Basically you have to make zillions of holes in the ground to put the seeds in, and you have to loosen up the soil around those seeds so that water will get to them, and so that they will be able to grow. One way of doing this is with just any strong stick, with a point on one end: you stick it in the ground and wiggle it around, and then drop a seed in, and you cover it loosely with dirt, then you do it again, and again, and again, all day long. These are called digging sticks.
But it's faster to use a plow. The simplest kind of plow is a digging stick with a handle on it crossways. You push it along through the dirt, so it makes a groove, and then somebody else goes along behind you dropping the seeds in here and there, and using her foot to cover up the seeds again loosely. You can make the plow go a little better by hardening the wooden point in the fire, or by adding a stone, bronze, or iron point to the stick, to act as a wedge.
Now, you can make a plow go faster, by adding leather straps or ropes to the front of it, and fastening them to a donkey or an ox, or two donkeys or two oxen, or even four sometimes. Now you push the plow while the animal pulls it. In heavier dirt, more like clay, which is common in river valleys like Mesopotamia, it may be impossible to plow without animals.
Finally, in the Middle Ages, somebody invented the harrow. A harrow is a wooden board that attaches to a plow, and helps the plow really turn over the dirt instead of just making a groove in it. Then if you harrow the field crossways after you drop the seeds, you don't have to cover the seeds up one by one anymore. Can you see the harrow here turning over the ground?