What is a sync speed for flash?

I have a Nikon D3100 and I'm looking to buy SB910, I'm doing online reading and research because I'm really interested in flash photography. I want to move a step further than the constant lights I have.
So my main question is what is sync speed and if so what's my camera's sync speed?

The shutter sync speed for most dSLR cameras is 1/200th, but you have to remember that the flash is only about 1/1000th second long, so the shutter speed does not matter unless there's too much ambient light

The sync speed is the shutter speed your camera needs to be set to so that the flash fires at the exact moment the shutter is exposed. If the shutter speed is too fast it will miss the flash. Your cameras sync speed is 1/200.

The D3100 max sync speed is 1/200 sec. This means that the flash, when it fires, is able to illuminate the whole of the sensor at this shutter speed.

Your camera's shutter consists of two 'curtains' (front & rear) - if the shutter speed is faster than the max sync speed, the second curtain will begin to close while the flash is still firing and you will get a black band appearing on your images (this is the second curtain closing).

When using flash, you can shoot at any speed SLOWER than the max sync speed - this will allow more of the ambient light in.

Remember - when using flash, FLASH exposure is controlled ONLY by the aperture, AMBIENT light exposure is controlled by the aperture AND shutter speed.

It is possible with compatible flashes to do high speed sync (HSS) - the flash is 'pulsed' across the gap between the front & rear shutter curtains, rather than firing in a single 'pop' - however, this requires the flash to be on nearly full power & close to the subject, as it uses a lot of power.