...and when to use it
Yuk! This is where you simply place the external speedlight on your camera, aim it straight at your subject and shoot or just use the camera’s built in flash.
It is sometimes unavoidable but if you can help it, try not to use direct flash as it is very unflattering and can wash out the colours. If you find yourself having no other option, at least use a diffuser on your speedlight to help diffuse the light and soften the shadows.
I have had no other option many times during wedding shoots where I had to use direct flash. One example is where the couple were cutting the cake as a fireworks display was about to go off behind them therefore they were out in the open (no ceilings or walls), it was dark and all ambient light was turned off.
I simply used my speedlight with diffuser safe in the knowledge that there were no walls behind to cast ugly shadows onto.