Yes, you might want to go to full manual, not A or S "manual" which is still a sense of auto adjusting. And ksmattfish is correct, that your camera meter does not give you perfect exposure. It gives you what 18% gray would be. It is up to the SHOOTER to determine from there what to do with that info... if you are shooting someone against a white wall, and meter the entire scene, do you think your camera is going to give you accurate exposure? Of course not. (*specifically if you are matrix metering the scene). It will be up to you to correctly change the exposure.
This poster specifically said that he is trying to auto focus in low light and having problems. Most cameras do, it is not a camera problem, but rather an APPROPRIATE level of light problem.