Mere Christianity

I just went out and bought Mere Christianity and a chronological bible ( yay me). I've read the first chapter of Mere Christianity, and I did not understand a word of it. C.S. Lewis doesn't actually use big words, but it's just the way he puts them together... I tried reading the 2nd chapter, and it made more sense, so hopefully it'll get easier. btw, what's a herd instinct? In the book they were talking about listening to your herd instinct and stuff like that...