In a nutshell (but go and read Fink for much more detail) base training is about building your endurance base, so lots of long slow stuff, time on your feet, time in the saddle, not worrying about distance. Its a little monotonous in that you don't feel like you have really killed yourself, but you feel fine to train the next day. It's all done at conversational pace.
Build is where you start inserting the speed, the intervals, the hill sessions etc.
Then peak is where you make your training very race specific, decent sessions at race pace etc.
Fink is great, esp for beginners. I'm just re-reading it.