This subject has been discussed so many times. Do a search for 'music notation software' here and on google.
There is a free program at:
http://www.finalemusic.com/notepad/It's quite good but a sort of taster for the more expensive programs made by finale. The next one up is Finale Printmusic.
I also use Noteworthy Composer which is a bit more flexible than Notepad.
There are a lot of programs around £30-£50. So many, I can't remember them all.
I've tried Lilypond but it's not exactly user friendly.
The advantage of Notepad is a 'Showcase' where you can download thousands of pieces.
For starters, just try Notepad.
Steve
Steve