Interstellar clouds, also known as nebulae, are vast regions in space filled with gas and dust. These clouds can be composed mainly of hydrogen, helium, and other trace elements. They play a crucial role in the formation of new stars and planetary systems, as they provide the necessary materials for star formation. There are different types of interstellar clouds, including molecular clouds, which are dense and cold, and diffuse clouds, which are more spread out and warmer. The density and temperature of these clouds can vary significantly, influencing the processes of star birth and the evolution of galaxies.