When you're first starting out with flash photography, one of the most fundamental skills you'll need is the ability to balance ambient and flash exposure. This great video will show you how to do just that so you can achieve the exact results you envision.
Coming to you from PJ Pantelis, this helpful video will demystify the relationship between shutter speed, aperture, flash exposure, and ambient exposure. One of the beautiful things about working with strobes is that you can decouple the exposure on your subject from that of the background. This allows you to properly expose your subject in front of a significantly brighter background without blowing the highlights in the ambient exposure (such as in outdoor portraits). It also allows you to darken the background while keeping your subject properly exposed, giving you the ability to isolate the subject in a way that wouldn't be possible without artificial light. In the video, notice how Pantelis' subject has the same exposure at all three shutter speed settings. This is because he's using the aperture to control the flash exposure and the shutter speed to control the background exposure. Grab a light and try this out for yourself.