What is an ISO value?
Shooting pictures in the dark without a tripod is not that simple. Depending on what you want to do, there is still the option about plying with the F-Stop.
If there still is not enough light, you have to increase the ISO value to create a hand held shoot.
Basically the ISO value contributes the photo- or light-sensitive of the camera. The higher the ISO value is the less light is needed to capture the image. This enables you to take pictures at low light.
If you increase the ISO value, you also increase the noise in the picture. Up to a certain point, Adobe Lightroom can bring it back to normal. There is no rule how high you can go with this. This pretty much depends on the camera itself. Just play around with your ISO values at your camera and you will figure out the at what value noise starts being visible in the picture.
High ISO value reduces the shutter Speed
If there is a low light situation and the F-Sop cannot be changed, the only option there is, is to increase the ISO value. Just keep in mind that the recommended level of the shutter speed is no smaller than 1/60 of a second. Everything below that will blur the image because your hand is not steady enough. This pretty much depends on the focal length. The wider the focal lens is, the easier it is to hold steady, the more you are zoomed in, the harder it gets.