My coin is too dark/light
As mentioned in the beginning, this has everything to do with metering; that is, how your camera determines how long to let the outside light shine on the sensor before closing the shutter. On many cameras the easiest way to get this done correctly is to use spot metering (or sometimes 'center weighted') because you're forcing the camera to determine the exposure based on the coin in the center and disregard the rest of the light in the frame. Still, getting an image that is too light or too dark proves to be frustratingly frequent and the only recourse is to manually adjust the metering to compensate.
Most cameras allow this in what your manual refers to as EV steps and are typically measured in halfs or thirds of a stop. Try bumping it a notch above or below and see if it gets you in the right direction. More advanced cameras accomplish this in one fell swoop by means of BRACKET METERING so that a single push of the snapshot button triggers three separate images each one offset a little in the hopes that one is properly exposed.
But how do I know when the coin is properly exposed?
At a simplistic level, your brain will interpret a properly exposed image when the darkest areas of the coin are pure black and the lightest area of the highlights are white. This is a bit simplistic and should be used only as a guide. In fact, if more than a few pixels of the highlights are pure white chances are that the area of the coin has been overexposed and this is usually the fault of the light source, not the metering. On the other hand, the opposite is true, a large area that is black and devoid of detail usually means that it didn't get enough light in the first place.
Shouldn't I just get a scanner?
It's definitely the easy way out and it's evidently what a lot of people use but nothing beats good optics when it comes to quality images. The main downside of a scanner is that it removes any control you might have on lighting. The scanner arm passes and lights the coin up as it goes along and you get what you get. And forget about getting razor sharp images. Still, as long as the scanner has a real light lamp and not an LED arm (usually the cheapest and thinnest scanners) it's undeniable that acceptable results are easy to achieve. Easy and mediocre or a long road ahead for the big payoff? Your call :-)
I think this about covers the basics. How enthusiastic you are about taking photos will ultimately determine how good you get to be a lot more than what brand your camera is which is what everyone gets hung up on. To many collectors taking photos is a chore and "good enough" is what they're aiming for while to others, like me, it's part and parcel of the fun of collecting.