I'll see if I can take this one, especially as I have a D50.
The meter in the view finder will only show itself in M, A and S modes. This is because in all the other modes the camera chooses all the relevent settings (except P where you choose the ISO, then the camera chooses everything else based on what it sees).
On the bottom of the view finder from left to right (lets use S for starters) you will see the following information:
*The diagram for focus section (which of the 5 spots the camera will focus on)
*Shutter Speed
*f/stop
*#of remaining exposures on your media card
Now, if the camera feels there is an acceptable f/stop available for the shutter speed you chose it will display that f/stop. If the camera feels there is not an acceptable f/stop the it will display either HI or LO along with the meter. You then need to adjust the shutter speed appropriately to get one of the "correct" exposures. The same would be true if you choose A (aperture priority).
If, in either mode, there is no possible way an appropriate reading can me made it will only show HI or LO, it wont show the meter. This may happen for example in aperture priority. Your maximum f/stop at 70mm is f/4.5 and the camera feels that there isn't acceptable shutter. It looks as though (in my little unscientific experiment) that it wont go below 1/20th. You'll then have to switch to Manual and use the meter. It seems as though the camera is telling you that you shouldn't hand hold the camera below 1/20th (total speculation on my part, but it sure seems that way)
In M (manual) it will show the shutter and f/stop and will always show the meter.
On the meter in this case you will see 0 with + to the left and - to the right. To get a "correct" exposure based on the meter you only want 1 bar to show. That is the 1 bar that will always show, directly under the 0. Any other bars to either side of the 0 and you have to adjust your shutter and/or aperture appropriately.
If you see all the bars showing to one side or the other and the meter is blinking that means that you are either way way over or way way under exposed based on the setting you have chosen.
You might also see the flash symbol blinking, meaning it is suggesting you use the flash in this situation (I'm guessing that is the case, haven't noticed it blinking when outside)
I'm giving this information based on looking through the view finder as I'm typing this out. I haven't read the manual recently, but I do use the meter quite often as I'm using shutter and aperture priority a lot more (especially aperture priority).
Hope this info helps.