Normally scientifically we have come to understand that the clouds are accumulated dust and water vapor. When the clouds become burdened with all of that moisture, they pour drain down upon the land.
Rebbe Nachman changes our perspective a little: He explains that berachah (blessing) only is revealed from a humble or hidden place. In order that blessings may descend from the heavens, HaShem first covers them with clouds so that the blessing can be revealed from its hidden source. We see from this perspective that the water in the clouds isn't the blessing itself, rather it is merely the means with which HaShem clothes the blessing, the blessing itself falls from the heavens.