A Matlab toolbox is a batch of functions dedicated to a specific purpose, e.g. statistical analysis. Most Matlab distributions contain a handful of toolboxes of their own; they can be accessed from the "Start" button at the lower-left corner of the Matlab interface. But once in a while you may need to install external toolboxes for usage in a particular area.
Days ago I came across the Econometrics toolbox for Matlab (different from the (other) Econometrics toolbox installed with the Matlab R2009a distribution; see help econ) which I need for my Honors Project. At first I couldn't figure out how I can use the functions in this package, and I googled but there was no relevant document either. Thanks to Amanda and others, I eventually figured this out.
First you need to move the folder of the toolbox to some domestic location; I would suggest Document\MATLAB on Mac machines where is the default folder for Matlab files. Then, from the menu bar, choose File > Set Path..., click Add with Subfolders... before choosing the folder of the toolbox (which includes all functions of it). Now you should see all subfolders of the collection you've chosen included in the list on the right. Save it, and now you should be able to command any function newly added like all other functions. Enjoy!