Read the tutorial. MetaStock comes with a tutorial section that gives you the run down on the program. The tutorial will cover all of the general aspects of the program and give you a basic run down of how everything works, but it will not give you much in the way of specifics. Reading this tutorial may not give you all of the knowledge that you will need, it will certainly give you a great place to start your MetaStock experience.
Surf around on the software's website. This will familiarize you with the aspects that the program uses. This makes it so that when you actually start to use the program, you will know where everything is and not have to search for it. When in the throes of observing stocks, it can be frustrating to not know where to find a certain piece of information. Surfing the software can give you an easy mental map of where everything is and how it relates to other parts of the website.
Practice. You cannot truly say you know how MetaStock works without getting your hands dirty. Start observing, tracking and analyzing stocks with MetaStock to really know how it works. You can read and look all you want, but it will never give you as much knowledge as experience will. Spend some time observing stocks before you put it to use tracking stocks you actually have money in. This will make you familiar with the software before getting into the real trading.