Answer:
Challah, along with the Challah board, and the Challah cover, symbolise the manna which the Jews received while they were in the desert for 40 years. On the Sabbath evening, the Jews would receive a double portion, so that they would not have to collect on the Sabbath day. That is why they have two challahs. There is a challah board, which is something under it, to represent the dew that fell underneath the manna, and the challah cover represents the dew that fell on top.