Impossible copy out files from my Mac to wd external device

Just bought a new “WD desktop elements” 3 TB… On windows ( home PC) all works excellent, but on my Mac book pro - comes message - “you can only read”, → I can’t get out files from my Mac to WD…

What should I do? Must I change some preferences? 

P.S… - on the pack there is information - Requires reformatting for Mac …  What does it mean?

u need to format the drive

http://wdc.custhelp.com/app/answers/detail/a_id/3865/session/L2F2LzQvc25vLzEvdGltZS8xMzQ5NzE2NTQ2L3NpZC82Tmo0YmQ4bA%3D%3D/kw/reformat/session/L2F2LzQvc25vLzEvdGltZS8xMzQ5NzE2NTQ2L3NpZC82Tmo0YmQ4bA==

If you want to use on both Mac and Windows the easiest way is some software for the Mac. This thread in post 6 has some http://community.wdc.com/t5/WD-Portable-Drives/unwritable-drive/td-p/435872 has some listed.

Joe