There are a number of reasons that the photos might be coming out underexposed. Did you set the ISO/ASA value to 200 on the camera? If not, it will over or under expose. With an old camera that you just started shooting the first non-technique thing that comes to mind is make sure the battery for the meter is still good. Meter something fairly average in bright sun, set the to ISO 200, and the aperture to f/16, and it should be showing a correct exposure around 1/200 (1/250) of a second.
What mode are you shooting in? Especially in shutter priority, it you might have it set high enough that the aperture can't open enough to properly expose the shot. If you are in manual, you need to increase the exposure for the shade. As a test, maybe set it to program for a roll, and see how those come out. If they are all (or most) exposed correctly, then it probably is a technique issue, if not, then something may be wrong with the camera.
Keep in mind that the meters in older cameras are usually center-weighted, meaning that they take an average mainly out of a circle in the middle of the frame. If you have something bright there it could cause the camera to underexpose the rest of the frame.
Since you said you were shooting outside, the green tint is probably something in printing, although it could also be expired film.