I know exactly what you mean now, @Sarah, by realistic!
I wondered long about the same thing, how to make a “picture look like what I see in real life, with my own eyes”, and still do wonder sometimes. 🙂
First, I must say that it is not always possible to capture what you see, straight from the camera. The camera is not nearly as complex as our created eyes. Sometimes it requires special equipment, or post-processing work, or taking control of light sources. The more you shoot, the more you’ll start to see what situations are easier or harder to capture as “realistic”, but setting caveats aside, here are two things to start thinking about every time you point your camera at something:
1. From what direction is Light coming from?
2. How is the camera reading that Light?
Is light coming from behind you? from the side? straight into the lens? a combination of directions? Is the light “ambient”, or indirect? How much light is each source creating? Are you in the shade? in direct sunlight? or under incandescent bulbs? Being aware of what type of light is around you is the first step to knowing how to take pictures like what your eyes are seeing.
Based on the type of light that is around you, you can start to guess how the camera will respond. In Auto or P modes, the camera will read the available light and automatically spit out a combination of settings that it thinks will create a “realistic” picture. It is using Automatic Exposure (AE). Under normal lighting situations, the camera will do a pretty good job: the camera will take a picture close to what you’re eye sees.
But what if it’s not a normal lighting situation? Say, sunset, or walking through a cave? That’s when the camera doesn’t really know what to do. The Automatic Exposure functionality isn’t smart enough to accurately read the light any more. So what do you do? That’s when people start moving over into the manual modes. If you know how to use manual settings, then your brain is what is actually in control and you can tell the camera whatever you want it to do. Using the manual modes, you are overriding what the camera thinks is “realistic” and actually creating pictures that are “realistic”.
I would start easing into shooting with manual settings by 1) doing what @Mr-Quebec suggested, start shooting in P for everything, and 2) start using Exposure Compensation to make your pictures brighter or darker (albeit accurately “realistic”) than what the camera suggests.
Depending on how well you know your camera, this should keep you busy for a while. 🙂