The second aliyah contains further preparations for the mabul:
Noach is to take into the ark seven pairs of every clean animal as opposed to only one pair of the unclean animals. Rashi says that the meaning of clean in this context means kosher for food. Rashi further explains that these clean animals would be used later by Noach for sacrifices to G-d. Rashi also says that the fact that Noach could distinguish between clean and unclean animals shows that he studied Torah.
The flood begins, according to tradition, on the 17th day of Marcheshvan 1656 years after Creation. Noach and his sons, and his wife and his sons' wives, and all the required animals boarded the tevah.
