We Sell Lulav and Etrog (esrog)
The mitzvah of waving the Four Species derives from the Torah. In Leviticus, it states: “And you shall take for yourselves on the first day [of Sukkot], the fruit of the beautiful [citron] tree, tightly bound branches of date palms, the branch of the braided [myrtle] tree, and willows of the brook, and you shall rejoice before the Lord your God seven days.” During the time of the Temple in Jerusalem, the waving ceremony was performed in the Holy Temple on all seven days of Sukkot, and elsewhere only on the first day. Following the destruction of the Temple, Rabbi Yohanan ben Zakkai ordered that the Four Species be waved everywhere on every day of Sukkot (except on Shabbat), as a memorial to the Temple
Historically, Sukkot commemorates the wanderings of the Israelites, which began with the exodus from Egypt (Passover) and continues with the giving of the Torah at Sinai (Shavuot) and ends with the wandering in the desert for the full 40 years as punishment for the sin of the golden calf.
A major agricultural festival, Sukkot is also the third of the shalosh regalim, or three 
pilgrimage holidays, when it was the custom of Jews everywhere to converge onto Jerusalem every Passover, Shavuot and Sukkot.
This is also why Sukkot is known as hag-ha-asif, the festival of ingathering. The Torah says:
You shall celebrate the festival of ingathering, at the end of the year, when you gather in your labors out of the field. (Exodus 23:16)
During the next century, when the Jews returned to Israel under the leadership of Ezra and Nechemia, they were ready to embrace the Torah's commandments. The Jews, ecstatic to be reunited with the land, built sukkot out of olive, pine, myrtle, and palm branches. The importance of Sukkot continued during the second temple era, with pilgrims coming to Jerusalem from Jewish communities all over. They participated in praying and singing and joining in the religious processions. The etrog and the four species- palm, willow and myrtle, which are bundled together to make a lulav - became part of the ritual.
To prepare the species for the mitzvah, the lulav is first bound together with the hadass and aravah (this bundle is also referred to as "the lulav") in the following manner: One lulav is placed in the center, two aravah branches are placed to the left, and three hadass boughs are placed to the right. (This order is the same for both righties and lefties.) The bundle may be bound with strips from another palm frond, or be placed in a special holder which is also woven from palm fronds.
Lubavitcher Hasidim place one aravah to the right of the lulav and the second aravah to its left, and cover them with the three hadass boughs—one on the right, the second on the left, and the third atop the lulav's spine, leaning slightly to the right. The bundle is held together with rings made from strips of palm fronds.
In all cases, all of the species must be placed in the direction in which they grew. (For the etrog, this means that the stem end should be on the bottom and the blossom end on top; this is the direction in which the etrog begins to grow, though as it matures on the tree it usually hangs in the opposite direction.)
The waving ceremony
To perform the waving ceremony, one holds the lulav apart from the etrog during the recital of the blessing. Right-handed users hold the bound lulav in the right hand and the etrog in the left hand. Lefties have differing customs as to which hand holds the lulav and which holds the etrog before the blessing is made. An Ashkenazi lefty holds the lulav in the left hand. A Sephardi lefty holds the lulav in the right hand.
Before the blessing is said, the etrog is turned upside-down, opposite the direction in which it grows. The reason for this is that the blessing must precede the performance of the mitzvah. Should all the species be held in the direction in which they grew, the mitzvah would be fulfilled before the blessing is recited.
A variant custom, followed by Lubavitcher Hasidim and some others, is to not hold the etrog at all while reciting the blessing, only afterwards.
After reciting the blessing, "Blessed are You, Lord our God, King of the universe, Who has sanctified us with His commandments, and commanded us to take the lulav" (the "Shehecheyanu" blessing is also recited the first time each year that one waves the lulav and etrog), the etrog is turned right side up (or picked up), and the user brings his or her two hands together so that the etrog touches the lulav bundle. The Four Species are then pointed and gently shaken three times toward each of the four directions, plus up and down, to attest to God's mastery over all of creation.
An additional reason for waving the Four Species in all directions alludes to the fact that all these species require much water to grow. The lulav (date palm) grows in watered valleys, hadass and aravah grow near water sources, and the etrog requires more water than other fruit trees. By taking these particular species and waving them in all directions, the Jew symbolically voices a prayer for abundant rainfall for all the vegetation of the earth in the coming year.
The waving ceremony can be performed in the synagogue, or in the privacy of one's home or sukkah, as long as it is daytime. Women and girls may also choose to perform the mitzvah of waving the lulav and etrog, although they are not required by Halakha to do so. Because women are not required to perform this mitzva, some are of the opinion that Sephardi women do not need to recite the blessing.
The waving is performed again (though without the attendant blessings) during morning prayer services in the synagogue, at several points during the recital of Hallel.
Additionally, in the synagogue, Hallel is followed by a further ceremony, in which the worshippers join in a processional around the sanctuary with their Four Species, while reciting special supplications (called hoshaanot, from the refrain hosha na, "save us"). From the first through the sixth day of Sukkot, one complete circuit is made; on Hoshanah Rabbah, the seventh and last day of Sukkot, seven complete circuits are made. As the Four Species are not used on Shabbat, there are variant customs as to whether hoshaanot are said and a circuit made on that day.
Symbolism
Several explanations are offered as to why these particular species were chosen for the mitzvah. The Midrash notes that the binding of the Four Species symbolizes our desire to unite the four "types" of Jews in service of God. An allusion is made to whether or not the species (or their fruits) have taste and/or smell, which correspond to Torah and good deeds. The symbolism is as follows:
* The lulav has taste but no smell, symbolizing those who study Torah but do not possess good deeds.
* The hadass has a good smell but no taste, symbolizing those who possess good deeds but do not study Torah.
* The aravah has neither taste nor smell, symbolizing those who lack both Torah and good deeds.
* The etrog has both a good taste and a good smell, symbolizing those who have both Torah and good deeds.
A second explanation finds the four species (4 mineem) alluding to parts of the human body. Each of the species or its leaves is similar in shape to the following organs:
* Lulav – the spine
* Hadass – the eye
* Aravah – the mouth
* Etrog – the heart
By binding them together for a mitzvah, the Jew shows his desire to consecrate his entire being to service of God.
Selecting the four Species (four minim)
While all mitzvot should be performed in the best manner possible, hiddur mitzvah (beautifying the mitzvah) especially applies to the Four Species. The halacha is explicit on what constitutes the "best" in each species. To that end, people will spend large amounts of money to acquire the most perfect etrog, the straightest lulav, and the freshest hadass and aravah. Usually a father will buy several sets of the Four Species to outfit his sons, as well. Another custom for hiddur mitzvah is to, depending on your custom of wrapping lulav and esrog, is to have more than two aravos and three haddasim. Some people have the custom to have as many as 40 extra haddassim and aravos.
Hiddur mitzvah applies to all mitzvot, but its absence does not impede the mitzvah from being performed. For the Four Species specifically, there is a further "technical" requirement of hadar (beauty), which does impede the mitzvah of the Four Species from being performed. Despite their similar names and details, these two requirements are distinct from one another.
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