The meter inside your camera generally right 80% of the time. It is that 20% that will vex and frustrate you though.
One of the most important things you need to learn is how your equipment works and why. The meter inside you camera is a “Reflected” light meter. It measures the amount of light being reflected back by whatever it is pointed at. Secondly it assume that everything is ~18% gray. When you point your camera at something it will tell you the correct exposure to make that something ~18% gray. So if you point it at a subject that is wearing a black outfit it will tell you the exposure to make it gray. If you point it at a scene filled with snow it will tell you the exposure to make it ~18% gray. Needless to say these are both extreme cases but in both the camera would be wrong assuming your goal was a faithful representation of the scene.
Here is how you can compensate. When metering with your camera in one of the more extreme situations point it at something known to be 18% gray that is in the same light as your subject. Green grass, sky 90 degrees from the sun are both about 18% gray. Another test you can do is take a reading from the palm of your hand. Depending on your skin complexion it can be plus or minus a full stop or so but once you know which it is you now have a good constant reference that you will always have with you.
Another thing you can do is use a light meter which is an “Incident” meter that reads the amount of light falling on the subject assuming you can take a reading of the light at your subject or at least the amount of light falling on them. I will cover light meters more in another article.
Here is an example of a shot that would typically cause an inaccurate exposure as the camera’s meter tries to make the snow more gray than white based on its exposure recommendation for a scene like this.