INTERVALS
An interval is the distance between 2 notes. There are 2 different types of intervals. If you play one note after another it is called a melodic interval. If you play 2 notes together it is called a harmonic interval. When you play the same note at the same time you are playing in unison.
Now, using the diagram below I will try to explain intervals. Each fret is 1/2 step. The distance of 2 frets is a whole step. A 1/2 step is also called a minor 2nd (see the diagram below). A whole step is also called a major second. Now here is a chart for you to relate the interval diagram to the chart.
Name

Distance

Unison

none

Minor 2nd

1/2 step

Major 2nd

1 whole step

Minor 3rd

1 whole step and 1/2 step

Major 3rd

2 whole steps

Perfect 4th

2 whole steps and 1/2 step

Augmented 4th / Diminished 5th

3 whole steps

Perfect 5th

3 whole steps and 1/2 step

Minor 6th

4 whole steps

Major 6th

4 whole steps and 1/2 step

Minor 7th

5 whole steps

Major 7th

5 whole steps and 1/2 step

Octave

6 whole steps

Note: Sometimes the Augmented 4th / Diminished 5th is called the Tritone.
The diagram below shows the intervals for going along one string down the fretboard.
