Go into your camera settings, pick the photo (i.e. Not video!) options and set it to take jpeg+raw in 4:3 format (not 16:9). For simplicity, set colour style to something like d-cinelike, and your white balance to suite (say sunny or cloudy). Set to take a single image (or a 3 or 5 multi exposure).
Raw+jpeg means you will get two files for each still photo you take... one jpeg which is pretty much a ready to use good rendition of the scene, but for which the file size will be less than 20Mb. That doesn't mean it's not a 20Mpix image. The raw file (DNG) will be closer to 20Mb in size, and will have e same pixel dimensions as the jpeg. but, you will need something capable of processing the DNG. The DNG file can be tweaked using software to give a much higher quality final image, and you can change the exposure etc in post processing without degrading the image as much as you would if you did the same to the jpeg.
Set 4:3 for photos... that way you use the full sensor size (aka 20Mpix) for the photo. 16:9 simply crops the top and bottom and gives you less than20Mpix... cropping is a post processing choice, so always better to give yourself the crop choice and shoot everything in 4:3.
Colour as d-cinelike, simply because it gives a reasonably pleasing color in the jpeg, it's not important for the DNG raw as you can tweak that in post processing easily.
White balance, set to the appropriate light condition simply so all your photos from the session have a similar colour balance and don't vary from shot to shot as they might if you used auto white balance. Maters for jpeg, but not for raw as again it can easily be tweaked in raw processing.
Single image, as it says on tin

. Or...
3 or 5 multiple images... if you set this, then every time you take a photo the camera will take additional photos for you... it automatically under exposes and over exposes the additional photos... it's kind of a hedge against you getting the exposure wrong. The extra images can also be used in post processing to blend the different exposures together to give a greater dynamic range - e.g. At sunset to balance the sky and shadow exposures.
Hope that helps.