Hello! De Vacas published two major works, Relacion (or Shipwrecks) and Commentarios. The first describes the failed Narvaez expedition to North America (out of 500 men, only de Vacas and three of his colleagues survived the expedition). The second work describes de Vacas's experience as the leader of an expedition in South America.
De Vacas's narrative offers details of North American species heretofore unknown such as the American bison, encounters with Native American tribes, and testimonies regarding the sometimes harsh terrain of the New World. De Vacas chronicles the privations, physical/mental suffering, and trials which necessitate their foray into the New World.
Sometimes, the men are attacked by Indian tribes (who seem to shoot arrows at them indiscriminately), suspicious of the threat foreigners might pose to their families. Indeed, de Vacas and his colleagues are often forced to depend on any food they find among the Indian tribes, even having to resort to fighting the Natives and taking women and children captive in order to obtain and bargain for adequate food sources. He describes a variety of cattle, fowl, and other wild beasts in his narrative. Despite the fascinating description of animal life, de Vacas' narrative is mostly centered on the thinly inhabited country and the harsh conditions of life in the New World. Lakes, dense forests, wastelands, and great deserts contribute to the challenging environment; biting insects such as different types of mosquitoes add to the misery.
De Vacas also describes the dangers and the trials of living at the mercy of Indians who have kidnapped them. He tells us about their strange diets and how the Indians sometimes assuage their own great hunger by ingesting what he considers inedible fare such as salamanders, spiders, worms, and even deadly vipers. Great fires built from damp and rotten wood are often the remedy of choice for the mosquito swarms. Unfortunately, the copious smoke often renders sleep impossible. De Vacas also describes the physical abuse he and his colleagues suffer at the hands of their Native masters (they were often kept up to tend to the fires and beaten if they were remiss in their duty).
Despite all their sufferings, de Vacas also tells of being held in great honor as healers by the Natives and he also documents various positive experiences with them. Although the experiences of the men in the New World were often filled with struggles, trials, and privations, each experience was an opportunity to grow and to challenge preconceived notions of the New World.
Hope this helps. Thanks for the question!