Inside the cloud are billions of tiny bits of dust and salt particles, which were carried up from the land and sea by the wind. There are also specks of water. This water meets colder air and condenses into the droplets that make a cloud. When the cloud is colder than about 15 degrees Fahrenheit, some of the water droplets freeze onto the bits of dust and salt, making ice crystals. Water vapor condenses onto these crystals, and they become larger.
Snow crystals are always six-sided because of the way water fits together as it freezes.
The snow crystals are tossed around in the cloud and more water molecules freeze onto them. When the crystals are too heavy to float in the cloud, they fall as snowflakes. During their journey to Earth, snowflakes change many times. They smash into each other, breaking pieces off, and colliding and sticking to each other. Snowflakes are also changed by the wind, by different air temperatures, and by moisture.