Part of worldbuilding is understanding the terrain. By definition, terrain covers all of the physical aspects of the world: mountains, canyons, plains, rivers, ponds and every other form of landmark you could imagine. Depending on your story, terrain itself may impact what characters can do when traveling. Regardless, terrain can have a massive impact on the ways and the resources people use to build their homes.
There are multiple types of terrain and each one presents unique challenges to life and civilization. Most of them also break down into smaller sub-types.
Mountains are frequent obstacles to travel. Their peaks also present challenges based around elevation such as lack of breathable oxygen, which reduces the amount of life found near the top. Mountain peaks also tend to be much colder. Both they and the slopes below have danger from avalanche and storms.
Slopes however are angled and cause water to run off. Because of their grade they make movement much harder. Hiking trails are often excellent examples of the sort of struggles you might face living on a slope daily. This unevenness also adds a challenge when building shelter. Slopes can also have rockfalls and mudslides collapse parts out from under them.
Valleys by contrast are often full of vegetation and life. These are the places where most mountain lakes and streams will eventually run to as they’re the low points between two mountains or mountain ranges. Although easier to travel through, they also have to contend with mass amounts of wind redirected by the surrounding mountains.
Forests have a larger variety of life and vegetation, which provides plenty of resources for your fictional people. Dense forests like rain forests and jungles having higher biodiversity. A medium or sparse forest will have less diversity in their flora and fauna, and sparse forests in particular may function as a transitional area between forest and other surrounding terrain. Regardless of the density fallen trees and undergrowth provide plenty of traveling obstacles while concerns such as fire create weather-related dangers.
Plains breakdown into two main types. Grasslands support larger animals such as bison, antelope and other herd animals, which in turn provide for larger predators such as lions and coyotes. There’s often smaller animals as well such as a mice and insects which attract their own share of animal predators. Flooding and wildfires are very serious weather concerns for grasslands.
Farmlands are often man-made plains. They may have been cleared out from another type of terrain, or converted from grassland. Because of the nature of farmland in which plants typically don’t remain where they are for more than a few years at a time (the exception to this being orchards), loosened soil adds in the threat of dust storms and soil erosion during rain.
Deserts are primarily defined by very little precipitation. Although the popular and most common form of them are hot and dry, there are also tundras to consider when thinking of deserts. These are cold places which have short growth seasons, reducing the amount of flora found there. Because of their temperature, exposure to the elements can be just as deadly in a tundra as it can in any other desert.
Sandy and rocky deserts are better known forms of desert. They are both hot, arid landscapes, but the difference is largely in the composition of the soil. Rocky deserts may occur closer to mountains where the mountains can block or redirect rainfall from reaching the desert beyond. Sandy deserts are often comprised mostly of sand and can form near rocky deserts, near mountains or towards the center of a continent and especially along equatorial lines. Dust storms and flash floods are very real dangers alongside exposure and dehydration.
Knowing what sort of challenges comes with your terrain helps understand what resources and struggles any civilization faces as well as finding suitable places for fictional animals.