Each car has different lights and therefore requires different bulbs. There's headlights, fog lights, brake lights, indicator lights, sidelights and interior lights - just to name a few! Along with all of the different bulbs, there are also different fittings, depending on your vehicle make and model. A fitting refers to the shape and size of the base of the bulb in order for it to correctly fit your vehicle.
You can also contact your vehicle manufacturer for the fitting information, or simply take a look in your vehicle handbook, which should state all the fittings that your vehicle needs for each type of light.
If you are a bit more hands-on and are able to remove your headlights yourself, you can remove the headlight and take a look at the bulb. The bulb will state the fitting around the casing i.e 'H7'. Take a look at this example: