Clouds are basically formed when a warm front and cold front bump into each other causing steam from water vapor. Just imagine a hot frying pan being splashed with water. Up high in the sky when the clouds become warm, it holds all that water in but when the clouds begin to cool down, it cannot hold the water as much and then the little liquid droplets come out and they have to go somewhere. While tiny drops are falling, sometimes they connect with other drops of rain and become bigger droplets.
Let It Snow
Snow starts in the atmosphere and condenses into droplets much like rain does. The more water vapor being condensed, the bigger the droplet gets. As the it gets colder, the droplets freeze and the more vapor collects, the heavier it gets. As it gets heavier, eventually the clouds cannot hold its weight anymore and presto! You have snow. Actually, the crystals that fall down from the clouds end up melting in a warmer atmosphere and when it melts, the other crystals will stick together; thus making larger flakes. It basically goes through a process of freezing and unfreezing on its journey down to earth.