I would like to know the meaning of the three matzot and why only the middle one is broken.
There are many explanations, meanings and innuendos. Here are a few:
Avraham served the Angles-disguised-as-men three loaves when they arrived at his home. That was on Pesach.
We compare the Matzah to "poor man's bread" an a poor man always puts some away for later, hence the "break and hide" routine of the middle matzah. Plus, hiding a piece of Matzah alludes to the Torah's instruction "You shall guard the Matzos".
Three matzas represent the Patriarchs, Avraham, Yitzchak and Yaaakov. Avraham was the man of Chesed (kindness and benevolence), Yitzchak of Gevurah (stern discipline) and Yaakov of Tiferet (balance and Torah study). Yitzchak's harshness needs to be broken to allow people leeway in their approach to G-d.
He also quotes "two of many" answers "on the level of derush. I'll leave it to others two write up their favorites from that category.