There are couple of different types of markers. I personally think anything can be an art marker. The difference between art markers and other markers is they are sheer and can be layered without totally losing the color underneath. Try a lighter value underneath and a slightly darker value of the same color family on top and see what happens. Also try using two complimentary colors (e.g. opposite colors in distance on the color wheel) to arrive at a wide variety of neutral grays You can come up with nuanced colors this way. They can be used very much like any medium, only difference is you don't have to wait for them to dry. They are alcohol based.
The other markers are Sharpies and I also use these. These work for more bold applications. You cannot get anywhere near as nuanced colors, but sometimes bright may be just what you want. Good luck!