I want to install Ubuntu next to my existing copy of Windows 8.
- How does Ubuntu affect an existing Windows 8 installation?
- How does the boot manager work?
- Will Ubuntu be my default OS in this case?
- Is it similar to Windows 7?
If you install Ubuntu to a separate hard drive, there's nothing to worry about.
Even on the same hard drive, as long as you don't touch the Windows 8's system partition, Windows should keep functioning normally.
Installing Ubuntu will also install the boot manager GRUB. Under normal circumstances, GRUB should configure itself and present you a list of operating systems to choose from when you boot.
If it doesn't, you can use Grub Customizer to configure it. See HOWTO: Grub Customizer.
Ubuntu will set itself as default choice on boot, but that's easily changed using the customizer.
No, not really. It might be visually similar, but it's quite different in the things that matter.
If you're still not sure if Ubuntu will work for you, you have two options before installing it: