What's the difference between a main star, a cluster, a galaxy, a nebula and a constellation? I have never used an astronomical telescope.

A cluster is a star system composed of many stars, such as the Pleiades cluster overhead. For example, we are in the Milky Way, which is very big. The stars in the night sky basically belong to the Milky Way, and the nebula is composed of interstellar dust, which is basically invisible to the naked eye. Constellations are artificially divided areas, which are composed of stars that look very close together and are associated with an image. If you study hard, you can buy a better pair of binoculars for only a few hundred dollars.