The fixture will tell you what type of bulb to use. You can't just put a halogen bulb in a fixture not meant for one. Take a look at the information on the box or in the directions to know the answer.

Tim, you are asking a very broad question. First, you need to consider the size of the can to get the right sized bulb. Then, you need to know the base type. Most likely, you will be using a medium based bulb which is the same base as a regular "A" shape bulb. The length of the neck should correspond to the depth of the can, however, some cans are actually adjustable. Typically you want the face of the bulb to be flush with the can, or slightly recessed. Your best option is to choose the light bulb the fixture was designed for and even then there are many choices. I recommend halogens because halogen light is sharp and crisp, unless you want to look at LED options. If your bulbs will be visible, you need to consider that some LED products don't look at all like standard incandescents. Do some homework on color temperature and CRI to make sure you get a pleasing color with enough light output. Halogen bulbs are interchangeable with regular incandescents and are not energy saving.