It is possible to take photographs indoors, without having to use flash, or artificial light,simply by utilizing the light from an open window or doorway and a white photographic reflector, or piece of white board, to bounce light back into the shadowy areas of your subject.
Ideal conditions would be a South facing window, or doorway, with the best light from about mid afternoon. Ideal, but not absolutely essential.
What will be essential though, is a tripod, or some device that will stabilize your camera in the low light conditions.
If you are using a digital SLR, set your aperture priority to about f5.6 (if you don't have the good fortune to be able to use aperture priority, then set your mode dial to "portrait" and that may suffice).
Try a few shots at f5.6, or there abouts and what ever shutter speed the camera adopts for those settings, but you may have to make a few adjustments as you go. Depending on the direction and intensity of the light source.
Keep the frame of the window out of shot, unless you particularly want to include it, but what you don't want to include is the bright, outside light, or your subject will turn out too dark.
For a moody head and shoulders portrait, have your subject facing the window, head turned slightly toward the camera, just enough to see both eyes, which should be looking at the camera lens, but be sure to centre your focus on the nearest eye.
Apart from people portraits done in this manner, and if it is really windy outside, or the sun is too harsh, you can photograph subjects like your pets, flowers, or insects indoors with this same method. Although, if you are photographing a bunch of flowers, you may have to set your camera to a smaller aperture to get them all in. (smaller aperture - higher number)