Transposition means moving every note in a piece up or down by the same interval, changing the key while preserving the melody and harmony. It's essential for vocalists who need songs in their range, instrumentalists playing with transposing instruments, and arrangers adapting music for different ensembles.
Decide the interval you need to move. For example, to transpose from C major to G major (up a perfect fifth), move every note up a perfect fifth. A C becomes G, D becomes A, E becomes B, etc. Adjust accidentals to match the new key signature.
Write the new key signature, then move each note to the corresponding scale degree. If the original melody in C major goes C-E-G-C (scale degrees 1-3-5-8), the same melody in G major goes G-B-D-G. This method is faster for diatonic music.
The best way to learn transposition is to do it. Take a simple melody, write it out in 2-3 different keys using our free staff paper, and play each version. Your brain will start to recognize the patterns.