if your computer was built/bought in 2013 or later). NOTE 2: Virtualbox may have problems booting Mac OS X if your computer uses an Intel Haswell processor (i.e. Type the boot flag 'amdfx' (also without quotation marks) if your AMD processor has 'FX' in its model name. NOTE 1: If your computer uses an AMD processor, you will have to type the boot flag 'amd' or 'amd64' (without quotation marks)- which flag you need depends on your specific processor, so test one flag at a time.
You will come up to the Niresh boot screen, with one option to select: OSX-Mavericks.