Infrared (IR) photography is about photographing those regions of the electromagnetic spectrum beyond the red end (from around 700 – 1000nm).
IR gives a very characteristic “look” to an image e.g. in landscapes. Green grass appears almost white, whilst other subjects such as coniferous foliage records very dark. It has been used to detect plant disease - healthy foliage will record lighter than diseased foliage for example, as well as various medical and forensic purposes.
You will need a camera capable of recording IR, probably a converted camera, and a suitable filter over the lens (see Camera Conversions).
A good filter to start with is the Hoya R72 or its equivalent. This will give a monochromatic (greyscale) image.
Many other filters are available, including dark red ones, which will record some colour, which can be used for creative (false colour) images
Daylight, tungsten or flash are all good light sources to use.
Exposure will probably be longer than for “normal” images, and you may need to do tests, using the camera histogram rather than use the camera in automatic mode.
The basic procedure for shooting with a full spectrum camera is to compose the image, place the opaque filter over the lens, and expose the shot. This makes it difficult to shoot subjects that may move. For this type of work it will be better to get an IR conversion specifically.