A pentatonic scale is any group of five notes that cover the span of an octave. There are literally hundreds of pentatonic scales in Western music, and hundreds more that use alternate tunings.
The Big Book of Pentatonics & Fourths will focus on the most common pentatonic scale, the major pentatonic and its relative minor. In the key of C the notes of the major pentatonic are: C D E G A. If you start on C and go up in perfect 5ths, you will get all the notes of the major pentatonic. The relative minor scale in A minor is A C D E G. If you start on E and go up in perfect 4ths, you will get the minor pentatonic in A.
Watch the video for more detailed instruction on how to properly practice the exercises.