Thank you very much!
I use mostly computer mouse but drawing grass is a little bit easier with graphic tablet.
I do sketches on paper and then scanning them to the computer. I use PhotoFiltre (which is free and hasn' got any layers. It's pretty easy for the start.) and Paint Tool SAI (this program has got layers but same easy) for coloring. I'm sure you can find these programs in the Internet. You can find a lot of tutorials of how drawing on Deviantart and in other sites.
Hope it'll help you! If you'll have any other questions just ask! I'll be happy to answer!

Good luck!