Portraits at night can be tough, as you may need a flash to provide enough light. However, ambient light around your subject can often be very atmospheric and something that you wish to keep in your portrait. Canon's full-frame mirrorless cameras such as the Canon EOS R6, which features a Dual Pixel CMOS AF II focusing system, can automatically focus down to EV -6.5, often allowing you to shoot without flash even in dimly lit conditions.
If you do use flash, Night Portrait mode, which features on most Canon EOS cameras, including the Canon EOS M200 and the Canon EOS RP, simplifies it all for you as it changes how your camera thinks. It will use either the built-in flash or register your Speedlite on the hotshoe to light your main subject and provide enough time for the ambient light to set the scene for your picture. It does this by using slower shutter speeds and automatically adjusting the flash time settings. Position your subject so they are lit by the flash, rather than the ambient light, and for the best results use a tripod to help reduce camera shake.
Bright conditions mean your portraits may end up with too much contrast. For those moments when your subject is backlit with strong sunlight, a flash can help. Either attach a Speedlite to the hotshoe of your camera, or set the built-in flash to fire for every picture. Your camera will work to balance the flash and daylight conditions for a much stronger picture where both elements – the person and the background – are optimally lit.
When using automated shooting modes such as Aperture priority (Av), or when using Auto ISO, you can quickly adjust for changing or challenging light using exposure compensation. While it may sound complex, exposure compensation is simply a way of making what's in your photo lighter or darker. It's particularly useful for capturing light skin tones to ensure your subjects don't look washed out, and for capturing darker skin tones that you want to look natural. Nearly all Canon cameras have an exposure compensation setting. Check your manual to find yours.