Night is seldom really dark, especially near urban centers that glow with street lights, traffic lights, vehicle headlights, porch lights, and security lights. These lights make the sky glow (and make seeing the stars difficult). This means we can often take photographs outdoors at night.
Also, camera manufacturers have made stunning advances in recent years in making sensors more sensitive to light. As of 2022, ISO values can climb as high as 200,000 in new cameras. The quality of the images made at these high ISO values may not be good, but they are getting better all the time. Sometimes acceptable images can be captured outdoors at night even when the camera is held by hand, especially if image stabilization is turned on. Many newer cameras do not have flash units built into the camera body. People rarely need them.
One challenge of photographing outdoors at night is that, because less light is available, long shutter speeds are needed. Then, holding the camera by hand is not a good option if you want detail and not motion blur (camera shake). The solution is a tripod or some other means of keeping the camera steady, to get rid of the camera shake.
In the photo above, the camera was shaken on purpose. At 1/3 of a second, everything is somewhat blurred.
Once the camera is held steady, very long shutter speeds are possible. If things are moving in the frame, they will blur at long shutter speeds or even disappear because they are so blurred. Objects not moving will be sharp and detailed (assuming they are in focus). Also, once the camera is held steady, ISO values can be lowered, often to their lowest values, ensuring quality images. If you have image stabilization, it is generally better if it is turned off. Otherwise wonky things may happen to your details as the camera tries to steady an image that does not need to be steadied.
In the photo above right, the camera was on a tripod and a flashlight illuminated the flowers one at a time over a period of 20 seconds.
An alternative to keeping the camera steady is to provide your own light on the subject. Using a flash is sometimes an option, if the subject is relatively close to the camera. Sometimes flash is a great option. Because the flash illuminates the subject for a tiny fraction of a second, motion is frozen. Also, because using a flash only lights subjects close to the camera, it illuminates those while keeping the background dark, nicely separating subject and background. Some flash units have manual controls to dampen their powerful lights and allow more ambient light to show in the image. This is worth experimenting with!
Often photographers use a tripod AND provide their own light, even outside at night. Flash can be combined with long shutter speeds. Also, a flashlight, spotlight, or other fill light can be used to emphasize parts of the scene, singling them out for extra illumination.