I belive Octave is a popular free/OSS alternative to MatLab? So where can I find some resource for learning how to use it? Perferrably videos but any will do.
You can freely download and install Octave on your computer. The download contains also a good documentation. Then you can search for more documentation for Octave and Matlab on the Internet. There is specially a lot of documentation for Matlab, and the good thing is that you can use it to a great extent also for Octave. And I recommend not only to read but also to try it out in your Octave.