Earths CLimate is determined by a number of things. The first of these is the lattitude of a given location. The farther north or south one travels from the equator, the colder temperatures become due to the decreasing angle of incidence (angle at which the energy from the sun strikes the Earth).
Another one of these factors is the elevation of a given location. The farther up one travels in the troposphere (the lowest layer of the atmosphere where earth's weather is found) the colder the temperature is. This is why the tops of mountains are often covered with snow; since the upper regions of the Troposphere are very cold, the precipitation that falls on mountains is often snow.
Large bodies of water (lakes, seas, oceans) also have an effect on climate. Since the airmass of an area is determined by the properties of the surface over which it formed, airmasses formed over water would be more moist (or maritime) than an airmass formed over the land (which would be hotter and drier)
Airmasses have a large effect on climate, and depending on where they came from determines their properties. Airmasses formed over polar regions are colder, airmasses formed over the tropics are warm and moist etc..
Mountains also effect climate. For example, the itlian penisula has a moderate climate even during it's winter. This is because the italian alps block the cold airmasses to the north, sheilding itlay from harsh winds. In contrast, areas of the Midwestern Contiugous United States (at the same lattitude as italy)have harsh winters because they receive similar polar winds but do not have mountains to the North to shield them from the harsh conditions of said winds.
Ocean currents also affect climates of coastal regions. Cool oceans give rise to cool winds, and vice versa, which can make an area warmer or cooler.
Cloud cover also affects climate. Clouds act as sheilds, blocking out the sun's light and heat energy, making temperatures drop during the daytime. Clouds can also trap heat in the Earths atmosphere warmer at night, an effect most notable during the cold winter months.
Vegetation can determine an areas climate, to a small degree. Vegetation like trees and photosynthetic plants make water vapor and shade, which can make an environment moist and cooler.
These are the major factors affecting the overall climate of a region. Keep in mind that climate is a very complicated and multi-faceted aspect of nature. Often, more that one of these factors weork together in a variety of ways to create the climate of a region. Thus, it is unwise to assume that a climate is determined by any one of these factors alone.