Do you want to write music? In the past, it was difficult to find notation software for less than $600. There are way too many options out there now, but almost certainly one of the best places to start would be MuseScore. There is also a good chance you might not ever need anything else!
Why MuseScore?
It's free. No downside to trying it.
Can do most functions of more expensive competitor software. It's not just new-to-music/kids using it, many professional musicians like it too.
It is the most used notation software in the world. There is a vote of confidence from a userbase... and there are a lot of places to find help, such as the forums.
MuseScore is probably the best notation software for sharing and collaborating in a Web. 2.0 kind of way. Of note, it is the largest source of free sheet music on the internet. In many ways because of this, using MuseScore is often the easiest and fastest way to make arrangements of tunes, as it can be possible to start with pre-existing sheet music (because of copyright, you might have to pay), which can then be modified as needed.
MuseScore is improving rapidly. The designers listen to feedback. Because of its open-source nature, it will not disappear or go out of business and there is a community invested in its continuous improvement.
Alternative Software (a few of the many choices in the ever-changing landscape)
1. Finale by MakeMusic (released 1988)
The traditional industry leader
2. Sibelius by Avid (released 1993)
The traditional alternative... They continue to drip out updates
3. Dorico by Steinberg (released 2016)
A modern alternative. After most of the Sibelius team was laid off in 2012, they were hired by Steinberg to work on a modern alternative software.
These 3 alternatives integrate with NotePerformer, the easiest way to get higher-quality sound out of Notation Software (which traditionally does not have great sound).
Increasingly, there are growing options of connecting Notation Software with Virtual Instruments for better sound.
Biggest Weakness of Notation Software
-Traditionally it is difficult to get high-quality sound out of notation software. The software that is used for recording both real and virtual instruments is a DAW (Digital Audio Workstation).
-It is likely that as the world modernizes, there might be some blurring of functions between notation software and DAWS.
Getting Started (as a Beginner)
From the Start Centre click Create New Score. Get through the prompts quickly then just start clicking! Messing around is the first step in learning functionality.
Look at other music creations others have made! From the start center click "Find Sheet Music", or from MuseScore.com click "Search for Sheet Music".
Next Steps in Learning (as a Beginner) :
Learn about basics of writing: 1. Melody
2. Bass Lines
3. Harmony
4. Drum parts/rhythm
Update: 25 Feb, 2023
-MuseScore version 4 is out! Updates from when I made this video with version 3.6, many improvements -Another fascinating alternative software could be NoteFlight. I have not had enough time to reasonably explore it, however, though it does not have the same userbase or open source advantage of MuseScore... It does however have the advantages of being: 1. Browser-based: Can be opened on any device without downloading software. This could be huge for many educational functions, especially where many schools now have Chromebooks but maybe not a separate computer-lab that is as easily available.
2. It is syncing with official publishers through Hal Leonard. So, official charts with publishing rights might be more easily editable.
3. Connection with ArrangeMe, if wanting to sell arrangements. -Some of Noteflight's more advanced features do involve paying, but it is free at basic level.