To get started you need only two functions -- 'setup()', which is called once at power-up, and 'loop()' which is called over and over whenever time is available.
To that degree the SFB exactly follows the approach of the Arduino project, which in turn built on the Wiring project.
SFB's are designed to plug together and 'talk' to each other easily, so one major difference is the SFB's approach to serial communications, which, in buzzwords, is 'packet-framed' and 'non-blocking'.
But that's less scary than it might sound. In practice, it means that serial communications is oriented around lines of text (a.k.a 'packets'), and the sketch can send ('print') and receive ('handle') packets without waiting ('non-blocking') for each byte to be transmitted or received. Very handy when you might be having four conversations at once!
Take a look at some Tutorials!