If you need to write down your scores and you want to use the computer, this wysiwig (What You See Is What You Get) will help you. It's exactly as using paper and pen, but with some help.
The interface of MuseScore is starred by panels and tabs full of notes, symbols and more. All of them ready to include in your masterpieces.
The editor features a lot of interesting options, such as capability to import and export of MusicXML and Standard MIDI Files, an integrated sequencer and FluidSynth software synthesizer, etc.
Finally, when you finish your creation, save it as many formats, including PDF and SVG.