Unfortunately, it is very unlikely that you will find a step by step guide to using LabVIEW and Octave together, simply because there just isn't that much demand for this. The link you provided is probably the most authoritive source for doing anything with these two.
Your best bet is to get in touch with Kaero. He wrote the VIs you are using, and he's mentioned in the comments of the post that he would like to get feedback from those who use his code.
Looking at the 3 x 4 example, I'm pretty sure you have neglected to set the Octave Exe File Path, and Script/Function Directory to the correct values.
The Octave exe file path should read:
C:\Program Files (x86)\Octave-3.6.2\bin\octave.exe (this is if you are running on Windows 64-Bit)
The Script/function directory should point to the place where you downloaded the multiply.m file. This is the file that defines the function. In my case, it was in my dowsnloads directory.
