Do I really need to buy live sand?

I apologize in advance if this question has already been addressed. I searched the threads, but couldn't find an answer that made me feel as if my question was answered.

So, I'm new to reef aquariums, and want to make sure I do it right from the start. I've got 90lbs of CaribSea Aragamax on its way, due to be delivered on Thursday. From what I understand, it is not live sand. I have a friend that just came back from Montego Bay, Jamaica and brought about 1/2 of a gallon ziplock bag of sand back with her for me. She brought it in for me on Monday, so it's really not old at all. I'm curious, can I use this sand to cure my tank, or do I need to buy a few 20lb bags of CaribSea live sand?

Also, I will be purchasing some live rock at a later date, but was told by my local pet shop, who has her own reef tanks, that I needed to cure my sand first, and then add in the live rock. However, from what I've been reading, I should be adding in the live rock first, to where it is resting on the bottom of the tank, and then add in the sand around it..? So, which is it? I'm so confused... :confused:

Thanks in advance for all of your answers/advice!!