What it is:
Creating sheet music so that others can perform it.
What you need:
Music notation software, such as Sibelius.
How you do it:
Enter the music into the software, either by playing it on a piano keyboard attached to the computer, entering it via a computer keyboard, or scanning and then editing existing sheet music.
Tips and suggestions:
Scanning often requires a lot of editing after the fact - it may be quicker to enter the music from scratch, depending on the length.