1. What are hoshanos?
When the Temple stood, huge willow branches were brought and leaned against the altar during Sukkot. The shofar was blown and the kohanim would walk around the altar and recite the prayer 'hosha na' - "Please bring salvation." Then the people would come in and wave the aravot (willows).
On the seventh day of Sukkot (the last day of chol hamoed), these branches were brought even if it was Shabbat, and the altar was encircled seven times. To remember this mitzvah in the synagogue, we walk around the bima once each day and seven times on the seventh day of Sukkot (Hoshana Rabba).
2. What is the procedure for hoshanos?
The ark is opened and one of the congregants removes a Torah scroll and holds it at the bima. The introductory four verses are recited, and anyone who has a set of species holds them while standing still. While reciting the following paragraph the congregation circles the bima counter-clockwise once, holding the species in two hands.
On Hashana Rabba, all the Torah scrolls are removed from the ark when encircling the bima seven times with the four species.
3. Is it permitted to hold the species in one hand?
In order to hold a siddur, many hold all four species in the right hand. However, if at all possible, it is preferable to hold them in two hands. The siddur can be balanced on the arms, or a lightweight copy used which can be held easily between the fingers.
4. What if a person does not have his own set of species?
Only those who are holding a set of four species should walk around the bima.
5. Who should hold the Torah scroll if everyone holds a set of species?
If there is a mourner, he should hold the Torah. (And it is a mitzvah for him to give his set of species to someone who does not own a set.)
If there is no mourner, someone should offer to hold the Torah instead of circling the bima. It is a greater mitzvah to hold the Torah than to circle the bima.
6. How are the hoshanos recited on Shabbat?
The ark is opened and the prayers are recited standing still, without taking the four species.
7. What is the special significance of Hoshana Rabba?
On Sukkot, God passes judgment on rainfall and additional prayers are said on this day to seal a favorable verdict. Additionally, it says in the Zohar that on this day all the decrees that were sealed on Yom Kippur are dispatched. An unfavorable sentence can still be torn up through a sincere repentance.
There is a widespread custom to read the entire book of Deuteronomy in the synagogue on the evening of Hoshana Rabba, and some remain awake the whole night to study Torah.
8. What aravah twigs may be used to fulfill the custom of taking a bundle on Hoshana Rabba?
It is sufficient to take three aravah twigs but most have the custom to take five.
Whatever is kosher for the aravah in the four species is also kosher for this mitzvah. In extenuating circumstances, it is sufficient to take one twig even if it only has one leaf. It is a hiddur to use long twigs.
The custom is to tie them with a lulav leaf or willow twig. According to some opinions, one may not use a leaf from the lulav that has been taken during Sukkot. If one has neither a lulav leaf nor a willow twig, one may tie the bundle with string or an elastic band, but the bundle should not be held at this place.
If one removes aravot from the lulav bundle, they may be used for this mitzvah. However, after they have been used, they may no longer be kosher to use in the lulav bundle. This should be taken into consideration if any other people may need to wave the lulav.
9. What is done with the twigs?
After the bima has been encircled seven times with the four species, the twigs are waved in the same manner as the four species but no blessing is recited. Some have the custom to wave them just a little.
Additionally, they are beaten on the ground. The bundle should be beaten five times on the ground. Preferably, they should be hit afterwards against a chair or any suitable object to remove some of the leaves, but not all the leaves have to be removed.
10. Can many people use the same aravah bundle?
The custom is to endeavor to obtain a separate bundle for each person, but if necessary several people may use the same bundle.
11. What should be done with the aravot after they have been used?
Some have the custom to put the twigs on top of the ark, while others challenge that this is disrespectful. In any event, they should be disposed of respectfully and many use it for another mitzvah.
Similarly, after Sukkot the four species should be treated with respect and not disposed of in the regular garbage. It is praiseworthy to use them for another mitzvah and many have the custom to use them as fuel in the fire when baking matzah or when burning the chometz on erev Pesach. It is permitted to use the etrog to make jelly.
Excerpted from "Guidelines - Succos" - 400 commonly asked questions about Succos (Targum/Feldheim).