Just a quick clarification of the middle gray idea - I don't know if it was clear from the previous post. The simplest (and somewhat oversimplified) way of looking at it is this:
Lets say you have a house with white walls, black doors and a grey roof.
Now you take a photo of it with B&W film using your meter. Lets assume that the house is pretty evenly lit (I think you will see how shadows fit into this by extension). Now, if you point your meter at the white wall (so it is ONLY reading the light reflected off the white wall - not the whole scene), it will assume that the wall is in fact middle gray. Now, if you expose as per the meter reading, give the film "normal" development and printing, your white house will be gray. The meter assumes that whatever it is pointed at IS middle gray. (part of the reason why most photos of snowy scenes look so mucky and... grey!). In this case, you would want to meter the gray roof - and the photo would then properly relate the other values.
This is the very, very basic of how it works. In reality, you would meter the door, so that you would have enough exposure on the darkest thing you still want to see some details of, then develop so that your highlights are controlled - but that is something that I think is getting a little bit ahead of ourselves. I think its something that you will discover the need for when you snap a few rolls. Keep in mind that most consumer cameras are set to take an average of the entire scene you see through your viewfinder - which works surprisingly well most of the time... but when it reaches its limitiations, it really shows. Many hand held meters are what is called "spot" meters - that is to say they take a reading of a very lmited area (imagine a cone 1 to 3 degrees starting at your meter), so that you can be very specific in what you want to meter.
I don't know if you are familiar with the theory, the basis of apperture and exposure time? I know its basic stuff - but we all had to learn it some time - I simply don't know how far along you are in this arcane knowledge!
As far as I know, most if not all light meters work on this principle - whatever they read will give you the middle gray - wether its reflected light (meter in your camera or one you point at the subject) or incident (one you place in front of the subject to meter the light actually falling on the subject and obtain you reading that way).
I know there are websites with content written by people much more qualified than I am - but I can't seem to find them in my favourites - perhaps someone could direct you. I don't know of any threads here on APUG that go in depth on the subject. I certainly recommend some reading - either on line, or the old fashioned way. Again, I really don't know which books would be best, I hope others will chime in!
Best of luck and welcome to APUG!