The way to use this combination of features is to select the area of your picture from which you wish to take your light meter reading, centre this area in the viewfinder and half-press the shutter. Either press your AEL button to lock the exposure or hold the shutter button while re-framing the shot, then press the shutter release button fully to take your picture. On some cameras AEL holds the exposure until pressed again, on some it holds for a pre-set duration of several seconds, while on others it holds until the shutter button is fully pressed. On some DSLRs the operation of the AEL control can be customised via the set-up menu. Look it up in your camera's manual to find out how yours operates.
For portrait shots, it's usually best to take a spot meter reading from your subject's face, since this will normally be the main focus of the picture. For people with average south-Asian or lighter Afro-Caribbean skin tones, no further adjustment is necessary. For typical Caucasian skin tones, add one stop of exposure compensation (+1), while for subjects with darker Afro-Caribbean skin tones, subtract one stop of exposure compensation (-1).
A useful accessory often used by professional photographers for making accurate spot meter exposures is the grey card. If you read the exposure tutorial I linked earlier, you'll have seen the chart of the zone exposure system. A grey card is literally that; a piece of card coloured mid-tone 18% grey, and you can buy them at any good camera store. Lastolite makes a particularly good one that folds up to pocket size and has a white reflector on the other side.
The grey card is temporarily placed in the scene you wish to photograph, positioned so that it is under the same lighting as the subject, and a meter reading is taken from the surface of the card by pointing the spot meter at it. For portrait shots you can get your subject to hold the card while you take a light reading. Once the exposure has been set the card is removed, before the picture is taken.
Some cameras, for example the current range of Olympus digital SLRs, have two extra spot metering options, highlight and shadow metering. In these modes, the meter is calibrated for zones eight and two on the zone system chart. In highlight metering mode, taking a spot meter reading from the most brightly lit parts of a scene will result in a correct exposure so that highlights are bright but with detail visible. Likewise using the shadow metering on the darker areas of the scene will produce dark shadows but with visible detail.