In music, Transposition occurs when we take a group of notes and move that group up or down by a certain interval. For example, if we take a C Major chord(the notes C, E, and G) and transpose them up by a Major second we then have a D Major chord (the, notes D, F-sharp, and A).

The step by step process by which we transposed a C Major chord up by a Major second to become a D Major chord is as follows:
  1. C Major chord: notes CE, and G

  2. Move the first note of the C Major chord, C, up by a Major second. We now have the note D.

  3. Move the second note of the C Major chord, E, up by a Major second. We now have the note F-sharp.

  4. Move the third note of the C Major chord, G, up by a Major second. We now have the note A.

  5. The results of transposing C, E, and G up by a Major second becomes:DF-sharp, and A, which is a D Major chord
As you can see all you need to do to transpose something is move each individual note in the group of notes by the same musical interval. With this method transposing becomes a simple process and we can then transpose any any note, chord, or scale.

Transposition is the movement of a series of notes, each the same distance. Transposing up or down one or more octaves is the easiest kind of transposition, because all the notes keep their same names when they are moved.

A Few Words About Transposing Instruments:
Transposing instruments are instruments that automatically transpose when playing - the actual pitches they play are different from what is written in the music. For example, the B-flat Trumpet transposes down by a Major second. For a B-flat Trumpet the written note C would actually come out as B-flat.