You have a camera and need a flash. They all look the same and seem to work the same but they are not the same. So, what happens if you choose wrongly. Simple answer, you fry your camera!!!
How do you avoid frying your camera. Well, buy a flash that is dedicated to your camera. Dedicated means that the flash talks the same language and uses the same voltages as the camera it's mounted on. If you are not sure of the dedication type that your camera needs, look at the hot shoe. The little metal contacts will be arranged in a specific pattern. Match the pattern you see to the pattern on your flash shoe. If they don't match, don't use the flash.
In some cases you can use as flash without the proper configuration if you are willing to give up advanced features. In these cases you must be sure that the voltage of the flash is not higher than the voltage of the camera. As a rule, modern cameras do not tolerate voltages higher than 6V. So, you must check the firing voltage on the bottom of the flash with a voltage tester while you press the test fire button. If it's above 6V, don't use it.
Older cameras with a single firing pin on their hot shoe can handle high voltages and will accept any flash without damage.
The best option is to match the pins, but if you need to use a questionable flash, refer to the following voltage guides and test the flash voltage before use.