Leviticus 23:39-43 discusses the Children of Israel wandering about after the Exodus, and God directs Jews to live in sukkot in commemoration. But it’s not just a matter of building the temporary home. God also tells His people to take “the fruit of goodly trees, branches of palm trees and boughs of thick trees and willows of the brook to use to rejoice before the Lord. These, then, are the arba’ah minim, or four species, that form the lulav and the etrog.
The lulav includes myrtle, willow and palm branches (in fact, lulav is Hebrew for palm (branch). The wonderfully fragrant but ridiculously expensive etrog (citron) is the fruit of goodly trees.
On Sukkot, Jews hold the lulav and etrog and stand in the sukkah, where (according to Ashkenazi practice) they first gently shake (or wave) the two to the east, then the south, then the west, then the north, and then up and down. The practice is repeated during the Hallel prayer.
Most families prefer to own their lulav and etrog—which is required, but only for the first day. After that, the arba’ah minimmay be borrowed.