As discussed in a previous post, one of the easiest ways to achieve a starburst is to close down your aperture to f/16 or f/22 or higher. However, if you are shooting at night and do not have the option of stopping down because you are hand holding your camera or if you have subject that requires a short shutter speed like a portrait then closing your aperture to f/16 or higher may be impossible. In these situations, you will need to use a star filter. Star filters come in different configurations, each filter will give different numbers of points. So if you want more or or fewer points, you will need to buy the filter accordingly. Why not just do this in post process - because a star filter will make every light source burst so depending on the scene this could be quite a chore to achieve in Photoshop.
Click here to see a sample of a star filter: