Ambient light as it is, is the light available in an indoor setting or an environment. Many a times, the ambient lighting is sufficient enough for us to handle it due to its low intensity which indefinitely leads to slow shutter speed and hand shake.
Of course there is the available ISO to be increased but then leads to highly excessive noise. Fret not! The use of external flash, if allowed is your key saviour. It allows you to shoot with better sharpness lower noise and still keeping your ambient light.
Let's say for shooting in a club! The lights go out, the spot lights come on. All you get is streaks of light shining on specific radius. Get your camera mode set to about 1/10s shutter speed and your desired aperture and then get your flash on TTL about -2/3 to -1 1/3 EV.
Start snapping away and enjoy great clubbing moment with great ambiance captured!