Matlab is an interactive package for carrying out matrix-based numerical computation, and for plotting data. Matlab does not do symbolic algebra. You can invoke matlab by typing at the prompt:
An interactive window will appear. You can type commands in the "Command Window" - the large window on the right.
A self-guided tutotrial of Matlab, as designed by M. Gockenbach at Michigan Technical University, is available via this link or its PDF. It covers all the basic features of Matlab, such as plotting, writing and running scripts and functions, and derived data types. Alternatively, there is one available with exercises. Ask the lecturer (B. Vorselaars) for details.