MuseScore is a free music notation program, similar in purpose to Sibelius or Finale. You create your score on the screen, and not only can you then print the sheet music out, you can export to MIDI or render the file as Ogg Vorbis (.ogg) to play or import into mixing software.
It being free software, the developers don't have an endless font of time and money to throw into development. Nevertheless, it does quite a lot... I find it meets my meager needs quite well. And, it has quite a good user community. One of the nicer resources is the MuseScoreHowTo YouTube channel. Short lessons, competently produced, to show you how to use the product. Here's one on how to enter triplets:
Even if you can't play a note and can't afford expensive software, you can, with MuseScore, create multi-instrument arrangements that will do you proud. You can find plenty of reviews of the product through Google, but keep in mind that most of them were examining early versions of the software.