OS X supports the option to read NTFS-formatted drives, but has not supported writing to these drives. Therefore, the use of a third-party driver such as Paragon NTFS or Tuxera NTFS has been required for those seeking full NTFS support; however, OS X does support writing to NTFS, but this feature is just not enabled by default.
To enable this feature, you have to do so on a per-volume basis, by editing the system's hidden fstab file to adjust the way the drive is automatically handled when attached and mounted.
First ensure that your NTFS drive has a simple single-word name, and then go to the Applications > Utilities folder and launch the Terminal program. In here, run the following command to edit the fstab file (supply your password when prompted):
sudo nano /etc/fstab
The Terminal should now show an editor window for the fstab file, in which you can enter the following all on one line. Be sure to change the word NAME to the name of your drive (it is case-sensitive):
LABEL=NAME none ntfs rw,auto,nobrowse
When finished, press Control-O to save the file, followed by Control-X to exit, and then unmount your NTFS drive and attach it again. When you do so, the system will no longer immediately show it in the Finder, but you can go back to the Terminal and run the following command to reveal it in the hidden Volumes directory where the system mounts all attached drives:
In the folder that opens, you should see the mounted NTFS volume, and should now be able to copy files to it, or otherwise manage files on it. If you need to access this volume more frequently, you can drag it to the sidebar, or make an alias of it in the location of your choice. You can also view the Volumes directory in Column mode to reveal it as a parent directory, from which you can create an alias instead of doing so on a per-drive basis.
Keep in mind that the writing ability of Apple's NTFS driver has not been thoroughly tested, and though this will enable write support using Apple's driver, there may be some limitations or unknown behaviors with the driver, so use it with caution. If you are dealing with important data, or need to access numerous different NTFS volumes, then third-party drivers may still be the best (if not most convenient) choice.