The important ones are Unattended Upgrades and snapd. The others are optional.
Unattended Upgrades (auto-updates) automatically handles deb package security upgrades only. You don't need to tell your Ubuntu system to run it; the system will quietly check automatically each day.
Snapd automatically handles Snap package upgrades. You don't need to tell your Ubuntu system to run it; the system will quietly check automatically each day.
Livepatch is an optional service and application that updates the currently-running Linux kernel. If not using Livepatch, you should reboot your system roughly every three weeks to update to a newly-released kernel.
Software Updater (formerly known as Update Manager) is an optional application that handles all deb package upgrades from all known sources, including kernel updates. That's much broader than Unattended Upgrades. You set the Software Updater frequency using the Software & Updates control panel. software Updater will remind you when it's time to review proposed upgrades. If you don't use Livepatch, SU will also remind you to reboot every three weeks or so after a new kernel deb is installed.
SU is installed with your Ubuntu system and turned on by default. It's 'optional' in the sense that you are not required to use it. You can use other tools (Apt, Synaptic) instead.
All deb package tools (apt, aptitude, apt-get, synaptic, Unattended Upgrades, Software Updater, Ubuntu Software, etc.) use the same tools and database under the hood. For example: If you use Software Updater to install security packages, it won't confuse Unattended Upgrades.
This is a slight oversimplification for beginners, just to get you on the right track. Many of these tools can be used more powerfully or more expansively...but at the risk of (serious) unanticipated consequences. As you learn your system, our advice is to simply use these tools the way they are intended to be used. The default settings are safe and sane.