Manual is not the answer for every situation. A dark scene needs more EXPOSURE. Check out those links I posted on exposure in your thread on how to blur background.
There are different things you can do will bring about more exposure. Trust your meter though for now. You need a wide (low number aperture) and/or a slow shutter speed and you may need to raise iso so your camera is more sensitive to light. Or add more light to the scene. Window light, room light, or your flash. Shutter, aperture, and ISO all come together to make a good exposure.
Your meter will help you with this. You could try shutter priority, set it for the lowest safe shutter speed to avoid camera shake. Depending on your lens, that might be around 1/30 or faster. The camera will pick the aperture. If the camera is not happy, you may need to raise ISO until the camera meter is happy and it can choose an aperture to balance with your shutter speed. Stay away from manual until you fully understand how exposure works.