Steam rising from a pot of boiling water or a hot bath is a cloud.
When it's really cold outside and you can see your breath, you're seeing a little cloud. The ones in the sky are formed when moisture in the air is cooled. The air around us soaks up moisture from rivers, lakes, and oceans. When the warm air close to the ground rises and meets cooler air above, the temperature falls and microscopic droplets of water are formed. This process is called condensation.