The Torah commands us to celebrate the Feast of Booths (Chag HaSukkot) for 7 days, from the 15th to the 21st of the Seventh month often called Tishrei. These holy days are also known as  "Feast of Tabernacles". No work is allowed on the 1st day of the seven days. Sukkoth is one of  three Pilgrimage Festivals which means every Jewish male is required to come to Jerusalem during this 7 day period. Although most laws in Torah apply to men and women alike, this pilgrimage law is only for  males. However both men and women are required to dwell in a Sukkah (Tabernacle) for all 7 days of the Feast whether they are at home or in Jerusalem.

First We Build a Sukkah:

The Torah requires us to build a Sukkah on Chag HaSukkot. Torah does not say however, how many walls, how big or small it must be. All we are told is of what materials the Sukkah must be built. 

The Torah requires in Leviticus 23,40 that we take on the first day of Chag HaSukkot  either the fruit of a splendorous tree  date branches, the branch of a thick tree and willows of the creek.  We are told in book of Nehemiah 8 that we are to have a national gathering. The Torah must be read to the people.

"And they found written in the Torah that YHWH commanded through Moses that the Children of Israel dwell in Booths (Sukkoth) in the Seventh month. And concerning that which they heard [in the public reading] they passed a voice through all their cities and Jerusalem saying 'Go out to the mountain and bring olive branches and oil tree branches and myrtle branches and date branches and branches of thick trees to make booths, as it is written.' And the people went out and they brought and they made for themselves booths, each man on his roof and in their courtyards and in the courtyard of the House of God and in the broad areas of the Water Gate and the broad areas of Ephraim Gate."

 In the book of Nehemiah the "four species" are to be used as materials for building a Sukkah.  Neh 8,15 speaks of using the four species of trees to build a Sukkah.  They read Torah, specifically, Lev 23:40 and  understood it to be commanding the using  the four species to build the  Sukkah. 

Compare the two passages in Lev 23 and Neh 8 and it will become clear that there are 4 categories of trees that may be used to build a Sukkah.

1.    Any leafy tree shade tree ( Ez 20,28).

2.    A date palm or other palm tree

3.    Fruit trees of any kind ( Lev 23 and Neh 8)

4.    According to Karaite-Korner Number 4 is described as:     Arvei Nahal - usually translated as "willows of the creek". Based on Neh 8 which replaces "Willows of the Creek" with "myrtle branches" it would seem that this refers to various types of trees that grow along the banks of the Wadis (see Isa 44,4) of Israel and Babylon (see Ps 137,2).

Shemini Atzeret

The 8th and final day of this 7 day Feast is a day of rest called in the Torah "Shemini Atzeret".  Shemini Atzeret , actually is not a  part of Sukkot. Thus the laws of the pilgrimage and dwelling in Sukkahs do not apply to this day. No work is allowed on Shemini Atzeret since it is a rest day.