If I use:

script.grandExchange.buyItems(GrandExchange.Box.BOX_3);

 

It opens up grand exchange box 3, but then:

 

script.grandExchange.buyItem(itemID, string, int, int)

 

Box 3 and opens the first empty box. I don't see anything for buying where I can input the desired information after box 3 is already open, can someone please let me know what I am missing?

BuyItem does everything for you and uses the first available box to do it. BuyItems was the original method which only clicks "Buy" on the desired GrandExchange box. This means you can either have OSBot do everything for you, or you write your own GrandExchange methods. 

Gotcha, thanks for the clarification, at least now I can quit attempting to do something that isn't possible with the API!