Has anybody out there used  a 1500 mah turnigy . I want to know that after opening it. . Should I first charge it??

Irrespective of the "Brand" of the LiPo you should always fully charge it and then use it only till 3.5v per cell (or only till 3.8v to be on a safer side)
If one intend to use LiPo Packs safely and don't want it to get damaged then he/she must have full understating of how it works.
This video should help:

And always use a LiPo Alarm while flying. Here's why:
http://www.rcgroups.com/forums/showthread.php?t=2381375

Infact this goes for any rechargeable battery in any electronics, for good life it has to be fully charged for the first time before use and as mentioned for lips utmost care to be taken.