What is the relationship between nebulae, constellations and galaxies?

According to the size, it can be arranged as follows: star system (such as solar system)

Nebula-Nebula contains almost all expandable celestial bodies except planets and comets. Their main component is hydrogen, followed by helium, and they also contain a certain proportion of metallic elements and nonmetallic elements. Since the launch of 1990 Hubble telescope, it has also been found to contain organic molecules and other substances. Nebula looks like a cloud-like object, which is a kind of non-stellar gas and dust cloud.

Constellation-just the connection of several stars in a certain area in the sky. In the three-dimensional universe, there is no necessary connection between stars. Although they are very close on the sphere of the celestial sphere, they may actually be far away. Since ancient times, people have been interested in the arrangement and shape of stars, and naturally linked some stars with similar positions to form constellations.

Galaxy-from Greek, a galaxy in a broad sense refers to an operating system composed of countless star systems (including the stars themselves) and dust (such as nebulae). Referring to the Milky Way, it is a huge galaxy containing stars, interstellar gas, cosmic dust and dark matter, and bound by gravity.