The figure below shows a major scale as you would play it on a bass guitar. The bottom line is the low "E" string, and the top line is the "G" string. Think of the neck as being turned on its side, facing you, with the end of the neck being at the left-hand side of the diagram. The numbers in the middle of the neck represent the number of the fret. The first few numbers at the bottom of the figure represent which fingers should be holding the string down, and the exes represent the rest of the scale. The first note played in either a major or minor scale is always the tonic. In this case the tonic is A. The seven notes of any scale are numbered as such, 1, 2, 3, 4, 5, 6, 7, with 8 being the tonic, just an octave higher. It is important to notice that in this diagram, the numbers in the diagram DO NOT correspond to the numbers in the scale, they are fret and finger numbers.
Referring to the numbers in a major scale, it's important to notice that the third and fourth notes and the seventh and tonic notes are a half step apart, all the other notes are a whole step apart. To better illustrate what I'm talking about in a theoretical sense applicable to music across the spectrum, there is a site that shows the musical staff of a major scale here.
Below is a diagram of an A minor scale. Notice how it differs from its major counterpart: the second and third notes of the scale are a half step apart this time, along with the fifth and sixth notes of the scale. There is also a musical staff diagram of the A minor scale here.
For full diagrams of every bass scale regardless of the tonic, click here. For full diagrams of guitar scales, click here. Remember, because the four strings of the bass and the first four strings of the guitar are commonly tuned to the same notes, a bass scale and a guitar scale will involve the same fingering for the first eight notes or so. That's a big reason why scales are dealt with in the bass section of this site -- it is more economical in terms of space and it covers most of the same material.