grub2 - How to boot into Ubuntu after installing into a pre-installed Windows 8 pc?

I recently just installed Ubuntu 13 from a USB drive.
I have/had Windows 8 64 bit on my desktop computer.

When I restart and boot my computer, there is not an option that allows me to choose Ubuntu, it goes straight to Windows 8. I understand this is a common issue.

However, my main question is, how do I get to even GO INTO Ubuntu after it's installed?
I don't mind booting into Windows 8 at first, but how can I even choose to see Ubuntu now that it's installed?