All OctaveForge packages (this name will change as soon we have [http://agora.octave.org/ Agora] online
running) are hosted in [https://sourceforge.net/p/octave/code/11146/tree/trunk/ this site]. Here we discuss how you can contribute to the development of those packages. Lets say you have found a bug in a function of one package and you know how to fix it.
You can use this function in Octave if you copy on top of the old one (or rename the old one to *_old.m), but be careful because it may require other new functions. Anyway, you can get the latest and coolest version of any package from that site.
Once you have the newest version of the function, check if it still has the bug you found. If it doesn't somebody solved it already. If the problem still there go on
an fix it!
Once you have fixed the bug, you can send a patch with your changes. How do you this? Check the [http://octave.sourceforge.net/developers.html developers help] page.