The constellation of Pegasus the Flying Horse has a convenient shape as part of it. The "body" and "wings" form a nearly perfect square from four, 2nd magnitude stars. This square is about 15 degrees per side, so that makes it easy to identify several other constellations from it.
The Great Square of Pegasus can first help amateur astronomers find Pegasus. When the square is crossing the meridian as seen below, the "nose" of Pegasus is facing towards the west (towards the right in the graphic below). That "nose" star is Enif, and for many observers facing south, the "head" will then appear to be upside-down from that perspective. The feet are "above" the head in this orientation, due to the upside-down orientation. Note how it appears here in this graphic:
Note the brightness of the four "square" stars, along with the nose star of Enif. These are all 2nd magnitude stars. Going towards the east/northeast, there are a couple more 2nd magnitude stars that direction. And the next two of these 2nd magnitude stars are also about 15 degrees apart. In fact, the upper right hand corner star of the Great Square of Pegasus does not technically belong to Pegasus. It is actually part of Andromeda, the Chained Princess. There is a slight bend on the first hop; this star is midway between the first two 15-degrees-apart stars, and is a full magnitude dimmer, at magnitude 3. Note the graphic below to see these three 2nd magnitude stars all about 15 degrees apart, and the one 3-rd magnitude star:
Following the line of Andromeda's brighter stars, making 15 degrees "hops" each time, takes the observer to yet another 2-nd magnitude star: Mirfak, in Perseus the Hero. Perseus is shaped like an upside-down lowercase "y" and is composed of mostly 2-nd and 3-rd magnitude stars. Look for Mirfak at the intersection of where the upper part of the "y" meets the lower section, as seen in this graphic:
But the Great Square of Pegasus can be used to find other constellations not connected to it as well. Following the "upper" line of stars that we used to locate Andromeda, draw a 25 to 30 degrees long line straight across those top stars. This brings the observer to a pair or 2-nd and 3-d magnitude stars very close to each other. This is Aries, the Ram. While this constellation does not resemble much of a ram in the sky, it does contain two First Light Guide objects worth observing. Check out the chart below to see how to find Aries from Pegasus:
And lastly, look diagonally across the square, from Andromeda, to the star where the "neck" forms the beginning of the horse head of Pegasus. The diagonal distance across these stars is about 20 degrees. Extending that line another 20 degrees in the same direction finds the observer at the two brightest stars of the largely dim constellation of Aquarius, the Water Carrier. While the constellation is large, these two stars are the important ones to help observers find the First Light Guide object nearby. See this chart to look at most of how Aquarius appears, but pay special attention to the bright stars at the head and right "arm" of the water carrier.
And that is how to find 5 constellations from the Great Square of Pegasus! Don't miss all the great objects you can find and see with a small telescope that reside within these shapes in the sky.
Check out the First Light Guides starting page to learn what you can find and observe by hopping to Andromeda, Perseus, Aries and Aquarius from the Great Square of Pegasus.