Cassiopeia is the Queen who boasted of her daughter Andromeda's beauty. She is the wife of Cepheus the King. Perseus is the hero who saved Andromeda from certain death from the sea monster. In the shape of a "W" or "M" these related constellations can all be found from Cassiopeia.
For observers north of 35 degrees latitude, Cassiopeia is a circumpolar constellation. That is to say, it does not drop below the horizon, but circles around Polaris the pole star. But she is best observed on the meridian when she is above Polaris, rather than between the pole star and the horizon. Polaris is the star on the meridian between Vega and Capella. Take a look at this chart, showing Cassiopeia crossing the meridian in an ideal observing location:
The western side of Cassiopeia has brighter stars than her eastern side. In fact, the lowermost star on the eastern (right) side is almost invisible in the graphic, and may be difficult to see from many light polluted areas. Look at those brighter, western stars, in the "M" shape. Note the outside two stars on the left-most side of the "M"; the upper one is Alpha Cassiopeiae and the lower one Beta Cassiopeiae. Follow that 5 degrees long line from Alpha to Beta, and continue it about two to three times as far past Beta, about ten to fifteen degrees. This places the observer looking right into the heart of Cepheus the King. Cepheus has mostly dimmer stars than Cassiopeia, but the brightest star of Cepheus - Alpha Cephei - is found directly from following that Alpha Cas to Beta Cas line.
See the chart here to learn how to spot the dimmer King from the brighter side of the Queen:
The princess daughter of Andromeda is found by following the same stars used to find Cepheus, but going in the opposite direction. Follow 2nd magnitude stars Beta Cassioopieae to Alpha Cassiopeiae, then extend that line up above Cassiopeia. The next 2nd magnitude star encountered will be Gamma Andromedae. From there, a line can be follow towards the Great Square of Pegasus. See the chart here for where Andromeda is in relation to Cassiopeia:
Now look at the central star of the "M" in Cassiopeia, the one at the bottom/middle. From here, go up to the right (east) towards the dimmer side of the constellation. The bottom one is Gamma Cas, the upper one is Delta Cas. Follow that line up and out from the constellation, opposite the direction used for Cepheus. A 2nd magnitude star - Mirfak, easily seen from most anywhere - is along that line. That is the brightest star in Perseus, the Hero, and it is at the intersection of the "y" shape of the constellation. Perseus is composed of mostly 2-nd and 3-rd magnitude stars. See the chart below to see how it looks compared to Cassiopeia:
And that is how to find 3 constellations from the Cassiopeia! 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 Cepheus, Perseus and Andromeda from the Cassiopeia.