So there are three things controlling light in a camera. Aperture, ISO, and shutter speed. These are called the exposure triangle.
Aperture is a literal iris in the lens that can be opened and closed to control the amount of light entering the lens. On a drone, and most cheap cameras, the aperture is fixed and cannot be changed. Aperture also gives you a depth of field effect at the larger end of the scale, while removing the depth of field effect with a smaller aperture.
This leaves you with ISO and shutter speed to adjust the amount of light hitting the sensor.
The general rule is that ISO should always be set to the lowest possible value. Increasing the ISO effectively amplifies the signal picked up by the sensor which in turn increases the amount of noise visible in the captured image. Noise will ruin a good picture which is why you want to be running ISO as low as possible.
The last value that can be changed in shutter speed. This is the literal speed the shutter remains open for, and thus the amount of time light can be captured by the sensor. A low shutter speed (ie 1/2) would open the shutter for half a second at a time, this will result in any moving objects captured in the frame being heavily blurred (because they moved while the shutter was open) but it will also let in the most light. A higher shutter speed (ie 1/1000th) means the shutter is only open for 1/1000th of a second at a time. This will result in far less (basically none) motion blur but also dramatically reduce the light captured by the sensor.