The exposure triangle consists of shutter speed, aperture, and ISO. Each of these 3 elements work together in creating an image. Aperture (measured in f stops) can offer different depths of field, including a shallow DOF with a low f number, and a deep DOF with a high f number. It also lets more/less light in depending on the setting, e.g. a low f number means the lens is wide open and therefore allowing more light in and vice versa. The shutter speed controls how long the lens is open for and how long the camera shoots the photo for. Measured in fractions of a second, a fast shutter speed like 1/360 freezes motion in the photo and allows you to capture fast moving things in focused detail, this setting also lets in a lot less light as the lens opens for a very short amount of time. Meanwhile a slow shutter speed e.g. ½ of a second, will create a motion blur effect capturing movement and motion trails while letting a lot more light in. Finally, ISO is how sensitive the sensor is to the light, a low ISO around 100 is less sensitive and therefore darker and a cleaner image, whereas a high ISO of around 1600, is more sensitive and allows you to take a well exposed photo in low/night lighting, however with a high ISO comes a grainier image.