Light meters read for the same value (middle grey), and pretty much operate on the same principle: input the ISO of the film, measure the amount of available light, and calculate a set or series of exposures. There are some techniques that can improve the use of meters, getting better (more accurate) exposures. These methods are pretty simple, and make a lot of sense.
Placement means metering a specific tonal area in a scene, and then adjusting the exposure to place it where you want it to be on the tonal scale. The most common usage of placement ensure that the important shadow details of a scene are recorded. While placement forms the first part of the Zone System method of exposure and development, employing placement alone will result in better negatives.
The first thing to do is to examine the scene. Determine where the significant shadow details are. The shadows are the thinnest part of a negative, and if they are underexposed you get nothing, as you can't make up detail that isn't there. Once the important shadows are determined, meter just those shadows. Using a built-in reflective meter (in-camera), fill the viewfinder with those shadow areas. It helps to throw the lens out of focus as well, blurring the tones together will get a better average reading.
If the camera's meter has center-weighted or spot mode, use it. These modes limit the meter's input to the center of the viewfinder, spot being smaller than center-weighted. Using a hand-held meter in reflective mode, the angle of view is usually around 25-30 degrees, so get in fairly close. If using a spot meter (such as the Pentax Spotmeter V), the small circle in the center of the viewfinder is what is being metered.
Once you have a meter reading, exposure value, or an exposure setting, the placement comes in. with our example, we are metering the important shadow details, intending to render then dark with detail on the print. Here we make use of zones, or tonal areas. Briefly, there are eleven zones, from 0, or paper black, to X (ten, Roman numerals are used), which defines paper white. Zone V is middle grey, which is what meters read for. Each zone is one stop difference from the previous or next.
We have metered our shadows, and we have a reading that will render those shadows middle grey. We want them darker than middle grey on the print. Zone III is defined as dark with detail, and is two stops from Zone V. To place the shadows in Zone III, we make the exposure at two stops less than our reading. This will render the shadow areas two stops thinner on the negative, which will print two stops darker.
The advantage here is that you are (more) assured of geting shadow detail rather than dead black areas. Since the shadows are the thinner areas on the negative, they are susceptible to underexposure. In most cases the highlights can be adjusted in the printing.
A grey card is a card that is colored middle grey. They are matte, and have an 18% reflectance. This is a specific neutral grey color.
The grey card essentially turns a reflective meter into an incident meter. Place the grey card in the scene, fill the viewfinder and take a meter reading. Since you are metering middle grey, simply use the metered setting.
Also called the Sunny 16 rule, the ƒ/16 rule says that on a sunny day, outdoors, of course, a good exposure is ƒ/16 @ 1/film's ISO. So with 400 ISO film, the exposure would be ƒ/16 @ 1/400th second. This can be rounded to 1/250, or 1/500. At 1/250 the exposure is over by about 2/3 stops, which is well within most black and white film's exposure latitude.