MuseScore is an easy to use graphical editor to typeset music scores.
You can use the mouse or keyboard shortcuts to add and edit staffs and notes. Several templates are available.
These screenshots give you an idea of the beautiful typesetting.
You can also play your compositions, either by outputting them as MIDI files, or by enabling sound during editing. The latter option requires the installation of a sound font.
You can download the latest version from the project web site.