Mac air notebook problem need help

I have a USB ex-HDD with NTFS format, I can send (drop) file from the ex-HDD to the MAC air notebook but I can send (drop) files from notebook to ex-HDD!! please help

If you want to save file from Mac to Ex-Hdd, you have to format it into Mac OS Extended Journalled, but IBM PC /MS PC will not able to read the content.
In NTFS format PC can write files Greater than 4GB，but Mac only can read the file but can't write into NTFS.
In MS-DOS FAT32 format both PC & Mac can read & write，but the file size is limited to <4GB.

but this usb ex-HDD is also need to use under win 7 system, so basic on what you need that I need to buy another USB ex-HDD for fat32 or NTFS but need to format to fat32

basically, A NTFS HDD can read by both Mac & PC, but only can write with PC.
A FAT32 HDD is compatible for both Mac & PC (read&write), but the file size is limited to less than 4GB.
to Fully use on Mac, you need to format HDD in

Mac OS Extended Journalled.

But PC will not able to read the content.

You may like to setup networking for both Mac & PC to share resource.

PC⇔Mac 如何互连，共享资料夹！

ok, totally understand!!do you know any website to show me how to setup networking for both Mac & PC to share resource.