The only way I'm aware of is to upload your already created files. Click "go advanced" when you want to post a chart or manuscript.
If you don't already have music writing software , there are several options available.
You can download Finale notepad, which I thinkis free, or SIbelius has a starter program that is relatively inexpensive. There are probably others.
YOu may have to convert your Finale of Sibelius files into pdf's but there are free downloads on the web that work well. I use
www.pdfforge.org.
LAstly, look around at some of the posts on this site. There are all kinds of things being posted. If you find something you like and want to find out how it was done, I'm sure that the poster would be happy yo tell you how they did it.