The pentatonic scale is made up of(of course) 5 notes. 2 types of pentatonic scales are found: the major pentatonic and the minor pentatonic.
The minor pentatonic is based on the minor scale. The notes are such(based on the minor scale):
A minor pentatonic A C D E G (A) I II III IV VI
The major pentatonic is based on the major scale. The notes are such(based on the major scale):
A major pentatonic A B C# E F# (A) I II III V VI I
You've probably heard of the blues scale. There are 2 such things. The pentatonic-blues scale is basically a minor penataonic played against a major chord progression(i.e. play a major A-E-D(I-V-IV) chord progression and play A minor penatonic against it)
The other is the blues box. It's illustrated here, as well as the common form of the major and minor pentatonic.
(all patterns here are transposable to other keys by moving the root note up and down the fretboard)
A minor pentatonic
E|-(1)--|-------|-------|---2---|
B|--4---|-------|-------|---5---|
G|--2---|-------|---3---|-------|
D|--5---|-------|--(1)--|-------|
A|--3---|-------|---4---|-------|
E|-(1)--|-------|-------|---2---|
5 6 7 8 Frets
A major pentatonic
E|--1---|-------|-------|--(1)--|
B|--3---|-------|-------|---4---|
G|-(1)--|-------|---2---|-------|
D|--4---|-------|---5---|-------|
A|--2---|-------|---3---|-------|
E|--5---|-------|-------|--(1)--|
2 3 4 5 Frets
A blues box
E|--(1)-|-------|-------|---2---|
B|---5--|-------|-------|---6---|
G|---2--|-------|---3---|---4---|
D|---6--|-------|--(1)--|-------|
A|---3--|---4---|---5---|-------|
E|--(1)-|-------|-------|---2---|
5 6 7 8 Frets