Open the Netbeans (my version is 8.1),
File > Project Properties > CSS Preprocessors > Sass tab
Configure Executables then into
Sass field if you already installed it or
Install Sass then you will be automaticly open [install-sass][install-sass] in your default web browser.
Then follow the instructions for install Sass on your machine(windows or unix).
Search and field with path to Sass filled automaticly or put it with your hands. Then back to window with preprocessors setting and setup
input /sass(or full path from project root folder) and
output /css (or full path from project root folder).
After this, your Sass that files stored in
input after save will be compiled to CSS that, in turn will be stored in
output, also you can disable auto compile after save and do it manually.