The camera tries to make the overall brightness of an image constant. But it also tries to avoid pure whites in the scene and may under expose to protect them. Have a read of this tutorial about the exposure metering of your camera:
https://www.cambridgeincolour.com/tu...a-metering.htm
You should then experiment with the exposure compensation and review your image and the histogram to check the settings.
I agree that you should reset your camera development settings to standard. Focus on the effects of changing picture styles (portrait, landscape, etc) and the exposure settings. To use the development settings requires a lot of post processing experience. By experimenting on a few shots in camera it will be hard for you to you learn how those settings change things. You should be able to apply similar changes in picture editing software. You can practice on many photos, compare settings on the same photo and get to learn the situations where you would want to use them.
Alex