Music Writing Software
When it comes to writing out scores for the site, I use Sibelius.
In the past I've also used Finale.
Both pieces of software are very powerful and take some time to learn. Please note, I can not give any help on this software and I'm only recommending it without warranty.
Both software packages have robust support channels on their respective websites.
If you want to write music on your iPad, I've have great success with the app Notion.