Intel(R) Galileo comes with a x86 Intel(R) Quark(TM) core which can run an OS. Hence in contrast to other microcontroller usecases where you program "baremetal" (i.e. w/o underlying OS) you typically make use on OS with Intel(R) Galileo.
That said - if you want to go through the exercise you can surely program baremetal. However, you would probably be on your own implementing all the various stages of x86 come up.