Whenever you see a scale, chord or fingering diagram, it is probably shown as a fretboard diagram. Fretboard diagrams are the simplest and easiest way to show information about notes on the fretboard of a bass or a guitar.
Layout of a Fretboard Diagram
Take a look at the attached diagram. This is a view of the fretboard as you see it when you bend your head down to look while playing the bass (assuming you are playing a right-handed bass). The four lines going across horizontally represent the four strings of the bass. The top line is the first string (the highest, thinnest string - aka the "G string") and the bottom line is the fourth string (the lowest, thickest string - the "E string").
Dividing up the strings are vertical lines corresponding to frets. The left side of the diagram is the lower side, closer to the nut and headstock. The right side of the diagram is higher, nearer the body. The frets shown could be anywhere along the neck. Some diagrams are oriented vertically, instead of horizontally. They work the same way, just rotated 90 degrees clockwise.
Many diagrams you see will have one of the frets labeled with a number to let you know where the diagram starts. Fret numbers refer not just to the metal fret, but also to the space before the fret where you would put your finger. The fret numbers begin with one at the bottom and count up towards the body. The example above begins at the first fret.
Reading a Fretboard Diagram
In this fretboard diagram, there are dots with numbers in them. Very often you will see dots, circles, numbers or other symbols placed on the diagram in this way. They indicate places to put your fingers.
This particular diagram is showing the fingering pattern for an A major scale. The numbers inside each dot indicate which finger you should use to play each note. This is a common use of numbers, but you may see them used for other purposes as well, such as scale degrees or note order.
Notice that two of the dots are colored red. As the key explains, this indicates the root of the scale. Since this is an A major scale, the root is the note A. Notice also the open circles on the left, past the edge of the diagram. These indicate that open strings are used in the scale as well. Any other unfamiliar symbols on a fretboard diagram will usually be explained in a key or in text below the diagram.