Hi, well congrats on joining the crafting community!
I use lots of different medium. I love my promarkers; they can give quick results or you can use different colour tones to build up layers, but I have also used pastels and glitter pens. All these should be available in your local craft store or online. Try lots of things though and don't be afraid to get it wrong...sometimes these produce the best results!
What I would say is stamp your image onto a separate piece of card and then you can mat and layer like the images you can see, then if you get it wrong you are only throwing away a piece of card and not a full card blank which is more expensive.
Good luck, I hope this is useful and happy crafting!