Travelling to Australia for 2 weeks. I downloaded google hangouts and have some confusion about using it in foreign countries:

1) Can I use to call from Australia to US and what is the charge?
2) Can someone call me on the number from the US and what is the charge?
3) Can I use it within Australia to make and receive calls?

Thanks
I have read much about this online and so far the only thing that seems definite is I can use it for calling Australia from the IUS at 1 cent a minute to landlines.

I have a Samsung Galaxy S5 from Verizon.