1. Create an empty directory test somewhere in the computer.
2. Copy the external library directory or jar  file to test.
3. Add the line Class-Path: <name> (where name is the library's directory or jar name) to the manifiest.mf file. If multiple items need to be listed, separate them with a space - not a colon or semi-colon.
CAUTION: The file  must end with a linefeed/newline, and as far as I can determine, the <name> can't contain spaces.
4. Build the Project in NB.
5. Copy the jar it creates (in the dist directory) to test.
6 From the test directory, either issue the java -jar <proggie> command or [in Window, assuming your machine is setup to do this] click/double-click the jar.