Composing is the process of creating new music. Throughout the common practice period and well into the twentieth century this consisted of a composer first imagining some new music and then writing it on manuscript paper using standard notation to create a score. Many composers used a piano or some other instrument during the process to test various ideas for melodies, harmony, rhythms, etc. and to evaluate what he or she had written. The completed scores were then delivered to an engraver for printing.
It is not clear how composers can imagine a new piece, especially long, complex works with multiple melodies and rhythms, and particularly counterpoint, just as it is not always well understood how new ideas are developed in other creative fields. However, it is likely that there are substantial differences according to the composer and even among different compositions by the same composer. In some cases ideas for new works have appeared in composers' heads seemingly spontaneously, in other cases composers have heard ideas for new works in dreams, and in still other cases composers have struggled to get ideas for creating new works or to refine their works in progress.
The process of composing changed dramatically during the second half of the twentieth century with the development and proliferation of low-cost electronic technology. In particular, scores are now usually created electronically using specialized notation software instead of writing them by hand on manuscript paper. And many composers, especially with popular music, create their music directly by recording live instruments and/or electronically, thereby completely skipping the score phase.