A sampler could be described as a device capable of recording and reproducing audio material, like a tape recorder. Unlike a tape or hard disk based recorder, samplers allows you to “play” the recorded sound via MIDI, using a keyboard for example. This way, any reproducible sound can be integrated into the MIDI environment, and be controlled from sequencers etc. like synthesizers.
The NN-19 is a sampler capable of recording and reproducing - but not editing - sound files.
There are also plenty of relatively inexpensive (and even free) audio editing software for both the Windows and the Mac OS X platforms, that will allow you to both record audio (via your computers or audio cards audio inputs), and to edit the resulting audio file. Virtually every software that is capable of this, can create sound files which can be loaded directly into the NN-19.