Primary location

 Hi,
I have some  doubts regarding the primary and secondary locations.

1.what is the use of primary location and secondary location in JDE Item availability.
2.how can i assign primary and secondary locations to an item.
3.If i  assign an item as a primary is it will pick automatically from that location while doing sales order entry,
4.what hapend when the quntity in the primary location finish..is it pick automatically from secondary location or i have to change the secondary to
   primary for picking the item automatically while doing sales order entry.

Thanks
Kishore