Read your manual carefully -- it will have a table of formats and of USB device types that the specific model supports. Some will accept a USB HDD, others will only accept a USB memory stick. Some can deal with NTFS, and others cannot. The newer it is the more likely that it will access a USB hard disk drive (i.e a HDD in a USB case).
The full manual for all Samsung TVs is available for download from Samsung support.
For example, I bought a new 40 inch a few days ago (UN40EH5300F) and it will use a USB HDD, although it is recommended that you use an external power adapter. I have a two year old UN55D8000 that can only use USB memory sticks.
You can also access the drive contents if you attach it to a computer and install the AllShare software that you can download from Samsung support.