NTFS is a file system, a way to store data on a disk. There are plenty of different file systems around. NTFS is the one created by Microsoft for their Windows machines.
There are two things you could do to solve your problem. Either present your removable disk in a File System read by MacOS, or teach MacOS to read NTFS.
First Solution
This solution is the quickest, but it presents two disadvantages:
1- You need to format the removable disk. Just like your friend said. In this case you will lose all the data already present on the disk.
2- When formatting, you get to chose a new file system. You will have to chose FAT32, a file system read natively by both Mac and Windows. Fat32 cannot process files larger than 4GB. If you're planning on send larger files, this is not a good choice.
Second Solution
There are softwares that teach MacOS how to read NTFS. I'm not an expert on Macs, so I'm not 100% sure on how good it works. I know the existence of project
MacFuse. I know that a while ago it was still considered unstable to use. If anyone can confirm that it works.
Conclusion
Chose which solution you would like best. Go on google to learn how to do it. We're here if you need more help.
[EDIT] I read
this review on MacFUSE. It basically says that MacFuse is great, works like a charm, but it could add some complications to your system (especially if you're using Bootcamp to dual boot with Windows). He advises to do it only if you know how to maintain your system alone. Don't forget that when you have any problem, you could always come here to find a solution.