Download QtOctave
There are a number of Open Source alternatives to the program MatLab, one of the most known alternatives is GNU Octave. When using Octave you use a command line to enter commands. For a novice, the lack of a graphical interface might be intimidating; QtOctave provides a somewhat user friendly graphical interface to Octave.
Web Interface to Octave
There is a cloud-version of Octave at http://www.verbosus.com/; from this place you can run Octave from the Internet.
Portable QtOctave
If you use Windows there is a portable version of QtOctave that can be downloaded from http://qtoctave.wordpress.com/2007/10/31/qtoctave-portable/. The neat thing with the portable version is that you can install it to a usb-stick; you can hence use it at schools that only provide useless computers. The downside with portable versions is that they tend to be somewhat buggy.
Using Ubuntu
Install QtOctave from Ubuntu Software Center.
Octave for Windows or Mac
QtOctave is just a graphical user interface for Octave. In order to run QtOctave, you must first download Octave, which can be downloaded from SourceForge http://octave.sourceforge.net/. Download it and install it.

Using Mac
First you need Qt which is a cross-platform C++ application framework. Download Qt from http://qt.nokia.com/downloads/qt-for-open-source-cpp-development-on-mac-os-x/; the file needed is encircled in the picture below, it is the "Cocoa"-file.

You also need the QtOctave-file which can be downloaded from http://sites.google.com/site/davidecittaro/software.

Double click on the zip-file to extract it, then move the QtOctave-file to the Application folder.
Using Windows
Download QtOctave from http://www.outsch.org/2011/01/29/qtoctave-0-10-1-for-windows/.

Download the zip-file from the link above. Right-click on the zip-file and
choose Extract all. Pick a place where you want the qtoctave-directory.
After extracting all files, go to the directory and then into qtoctave/bin,
find the file qtoctave.exe, this is the executable file, don't move this file.
You can make a short-cut to the desk top by right-clicking on qtoctave.exe.
When you start QtOctave for the first time you might get an error message saying
that it cannot find Octave; the program will start anyway but you will not be
able to do anything without Octave. Find the file Octave.exe on your computer,
the file is in a directory called bin (binary). Right click on
the file and choose properties to see the file path. It might look like this:
C:\Octave\3.2.4_gcc-4.4.0\bin
You must now specify this file path in QtOctave. Choose Config->General
configuration and click on Octave.

Click on Select... and navigate to the executable Octave-file.

You can also write the file path.

Note that Windows uses "\" to separate directories whereas Unix/Linux uses "/"!
Getting help
If you need help, Google on either MatLab or Octave plus whatever you command/feature you want to know more about. Most of the homepages are made for viewers having a mathematical knowledge exceeding that of a student at school. MatLab is an abbreviation of Matrix Laboratory and the program itself is based on matrices; you can however use the program even though you lack a deeper understanding of linear algebra, in many cases you can think of the matrices simply as tables of numbers.
by Malin Christersson under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 Sweden License