The best free IDE I have found for the discovery board is Atollic light, I tried others with less luck. http://www.atollic.com/index.php/download/truestudio-for-arm
You also need to download nearly all these PDFs. http://www.st.com/internet/evalboard/product/252419.jsp
You need to start reading, it will take some work.
Arduino is a lot easier in my opinion, but STM32 has massive speed and possibilities.