"Technology Nigh Perfection"
Long ago, someone who wanted to compose music absolutely needed to meticulously write down notes on sheets of paper, without being able to hear their song until it's finished. At this time, you also needed a quite impressive budget if you needed to showcase your songwriting capabilities. Fortunately, today we have computers! So in this entry, I will show you how to use your computer to compose music (for free of course).
This program is not necessary, but I strongly recommend it if you don't have any instruments at home. Click MusicalKeys is basically an electronic piano for your PC. It uses the MIDI interface to produce realistic sounds of dozens of instruments, that you can play with your keyboard. It's free, but do note that it's only available for Windows.
Now that we can play music, we need to write it. MuseScore serves exactly that purpose. Using the mouse or keyboard, you can drag notes onto a virtual music sheet and have it played back by the computer! You can edit anything from time signatures to instrument choice, and export it as many popular audio formats (*.ogg, *.flac, *.wav, etc.), or save the score to a *.pdf for efficient printing and redistributing.
After you're finished composing your music sheets, It's time to put all the parts together using a mixer, in this case Audacity. With it you can record, merge, mix, edit, and save music with just about as much flexibility as any professional tool.