The constellations are the 88 parts in which the celestial sphere is conventionally divided in order to map stars. The groupings thus formed are exclusively perspective entities, to which modern astronomy does not recognize any real meaning.
In three-dimensional space, stars that form the same constellation can also be separated by huge distances, as well as different sizes and brightness, conversely, two or more stars that appear very far apart on the celestial sphere, in three-dimensional space, may on the contrary be separated by distances smaller than those that separate them from other stars in their constellation. During a hypothetical interstellar journey, we would no longer be able to identify any constellations, and any stop near any star would make us identify if anything new ones, visible only from that new perspective. Over time, different constellations have been defined, some have been added, others have been joined together.
Have a look at this nice overview of all constellations with an interactive map. Also, the Messier catalogue is always worth visiting.
free 3D realtime space-simulation (OpenGL)
Stellarium: realtime sky with OpenGL
Strasbourg Astronomical Data Center Files on official IAU constellation boundaries
Interactive Sky Maps
Other references will follow.