A constellation is a group of five to twenty stars combined into a single unit. This group is usually assigned a mythical figure or an animal. These divisions began already in the Neolithic Age with the Zodiac Signs, in ancient times this was intensified. Seen from Earth, these stars, which have been grouped into a constellation, seem to be close together.
Information, mythologies, and sizes of all the 88 constellations and tips on how to spot them can be found here: https://www.star-registration.com/what-is-a-constellation