Protecting soil is mostly about keeping a healthy ecosystem in the area, and especially keeping plant root systems in place. Soil erosion, when the soil runs off the land due to wind or (especially) water, is very damaging and healthy plant roots can help keep the soil in place. Certain plant species that make partnerships with fungi and bacteria in the soil can help increase soil fertility.
A lot of modern farming practices are damaging to soil. Soil gets tilled, disturbing soil organisms like worms, fungi, and insect larvae. Running large tractors over the soil can compact it, eliminating tiny air bubbles and pores in the soil that help those soil organisms survive. Tearing out roots, and leaving the soil bare for long periods of time increases erosion. Fertilizers and pesticides can damage soil organisms.
Fortunately, there are other ways to farm that damage the soil less! Using cover crops, not tilling the soil every year, and planting many species of plants (with different root systems) can keep the soil healthy while farming the land.