system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What more megapixels give you and what they do not (or, why more megapixels isn't necessarily "better")
gpt
More megapixels means that you get images with more pixels.  This means you can make a larger image at a given resolution, or have better resolution for a given size.  Most people don't make prints large enough for this to really matter, as most cameras have plenty of megapixels.

More megapixels can be bad when you have to cram a bunch of them onto the camera's sensor.  This is a silicon chip that detects the light and makes the image.  If you try to squeeze in a bunch, you can limit the quality of the pixels.  For a point and shoot camera, it doesn't make sense to try to put in more than 12megapixels or so, because the camera's sensor is quite small.

A fancy DSLR will use a bigger sensor, some as big as 35mm film.  There are many reasons this can be better.  One of them is that you can increase the number of megapixels without degrading the quality of the sensor.  There are also optical advantages that allow for higher resolution.

None of this really matters, though.  There are other factors that are far more important than megapixels, like lens quality and skill.  Learning what sort of light is good for shooting or how to use fill flash will both get you better images than any number of megapixels.