When looking for a new flash for your digital camera, there are many options and price points and it can be a bit confusing. Before buying an external flash, consider the following points.
Does your camera support an external flash?
What you are looking for is what is called a hot shoe. This is a small square of metal usually on top of the camera with one to five or six metal circles in it. This is the interface for the flash.
If it has only one contact (metal circle), then your camera can use a manual external flash. If there are more then your camera is compatible with a dedicated (fully automatic) flash probably from your cameras manufacturer (check your manual).
If you have no hot shoe you could still get what is called a slave flash, which senses the firing of your built-in flash and fire as well. However you will likely be disappointed with this option as it offers little control.
Manual external flash (old school)
This type of flash has been made for years and years and may or may not include an auto setting. Be careful and find out the flash’s trigger voltage.
In the days before digital, cameras could stand high voltages from the flash some around 350volts. Modern digitals usually won’t handle any thing above 6-12 volts. If the voltage is too high, this can be a quick way to need to buy that new camera you have been wanting.
In manual, you are responsible for shutter speed and f-stop and flash power. Don’t be scared though because we have LCD screens on the camera. You can check the screen and know that it is too bright or dark and adjust.
For example, you would choose a shutter speed probably around 1/60th because this is just about as slow as most people can hand hold a camera with out getting camera shake. F5.6 because you want a little depth of field so that everyone will be in focus.
Now if they are patient you can take a series of photos and adjust the flash power until you get a good one. This will work but it is slow. If the flash has an auto mode it will likely want you to set a certain f-stop and then try to keep your subjects at a given distance.
Dedicated external flash
If you get the flash that is recommended by your camera manufacture then it is very likely that all you have to do is put the flash on the camera and turn it on. The computers in the flash and camera will do the rest.
Higher end dedicated flashes have more options like manual control, rear curtain sync, high speed sync and wireless functions. If your camera supports it this would be my recommendation.
If you have a compact and a DSLR by the same company, you may be able to use the same flash on both.