Flashes for dslr cameras?

What's the difference between the variety of nikon flashes? Arent all of them just for extra light?

i see on the website one of the flashes are like $800! And ones $100? What's the diffference between the both of them!

Yes, all of them is for extra light. Some just a tad little more than the built-in flash and some enough to fill the whole stadium. Not really but that's how varied they are.

Power output is a big part of it, but better flashes typically:

Have several modes from full auto to full manual and multiflash strobe.
High speed sync. A flash normally is somewhere around 1/20, 000 of a second… Very fast. A shutter has two parts, front and rear curtains. The fastest shutter speed in which the shutter fully opens (the rear curtain does not start to move until the front has fully opened) is usually around 1/200 of a second. Any faster shutter speeds require the rear to start before the front has fully opened. With very fast shutter speeds, the shutter curtains form a narrow slit that moves across the opening.

But I digress.while 1/2000 is very fast for a shutter speed, it is very slow for a flash and requires a huge amount of light output. High speed sync is very expensive for this reason.

Communication, better flashes can wirelessly control other flashes or groups of flashes. The better flashes and cameras can work together wirelessly and off camera, and can take exposure direction from the camera.

Reserve, burst, and recharge time are better with the more expensive units.

Flash is not my strong suite, I'm probably missing something. As with anything else, you get what you pay for and sometimes the expensive choice has features you never intend to use, so it makes little sense to get. I have a cheap flash I use with an optical slave occasionally, but I can light up a football field with my canon and sunpak working together.

Learn how to use your camera to it's fullest extent first before buying a flash. And it seems like you haven't even done any research, so don't waste your money, just get the cheapest one. I have the cheapest canon flash and it works fine for what I use it for