Unfortunately, the operating system does not recognize formatting that have been made with the NTFS file system. There are only recognized FAT32 file system properly and reliably by Android. Therefore, you should format the USB stick or memory card with FAT32. This is best done via the PC. So you formatted a USB stick with FAT32 and Windows.
1. recognized bury your removable storage device to the USB port of the PC, this is now
2. Click on "Computer" or "My Computer" and then right click on the newly added removable disk
3. Select the pop-up menu "Formatting" from.
4. In the window that opens, select "File System" in "FAT32" should be
5. Formatting the USB stick or memory card with the file system is formatted (Attention, all data will be deleted)
Then you can the USB flash drive again with the OTG cable and your Samsung Galaxy S6 connect. This should now detect the disk properly and allow access via File Explorer. Should not be the case, then it may be that your USB Stick requires an additional power supply. Checks by contacting in the specifications of your USB stick or external hard drive.