Transposing (or transposition) means changing the key of a piece of music. This can apply to a scale, a phrase, a short melody, or an entire song. The ability to transpose is an essential skill for all musicians to develop. The easiest way to transpose is to write the scale degrees under the original melody and then work out which notes correspond to those scale degrees in the key you want to transpose to. You should work towards being able to do this in your head instantly, without the need for notated scale degrees.
the following examples are a short melody played in the key of C and then transposed to the keys of F and G. Play through them and notice that the melody sounds the same, but the overall pitch may be higher or lower. Transpose this melody to all other major keys. You should also try this same technique with other tunes you know. The more you do this, the easier it gets, and the better you are at transposing, the easier it will be to play Jazz.