To get rain, the water condensing in the clouds has to become heavy enough to fall to Earth. The tiny droplets just aren't heavy enough to fall. Just like fog or in the shower, they go whichever way the wind and eddy currents blow them, or they just hang there, suspended in the air.To become heavier, the droplets need to grow into drops. To do this they have to acquire more water and become larger. Some will collide with other droplets and become larger, and others will grow as water condenses out the air directly into the droplet. Others will grow by both methods. It's a bit like watching drops of rain water on a window - small drops fall, they join with other small drops, become larger drops, and so on. In the right clouds, this process will be happening to millions of tiny droplets, all growing at the same time, but at different speeds.Eventually, if the droplets keep growing, they will reach a mass where they can't stay floating in the cloud because they are too heavy - and will start to fall. Some may get caught in upward blowing winds and get blown back into the clouds for a while, but once they are heavy enough to overcome the force of the wind, they will fall to earth - as rain! It will keep raining as long as the conditions are right to make the clouds and let the water droplets grow heavy enough to fall.So, there you go - now you know what a cloud is, and how it creates rain.
1. Convectional Rain