Shavout- Is the holiday when the Jewish people accepted the Torah and Received it.
In Israel those who live in Israel year around Shavout is only one day, outside of Israel it is two days.
One must light candles in honor of the holiday just like they would light before Shabbos. The bracha ends in Hadlik ner shel yom tov. One should also recite the blessing of Shechiyanu (women only) men say it in kiddush.
There is a custom that one should stay up the whole first night of Shavout to learn. Especially among the men, the idea behind it is, that you are preparing yourself for receiving the Torah. Also it says that during the time of the Torah giving in the desert, the Jewish people overslept, so we stay up the whole night as an atonement for this.
If one has stayed up all night, and has not slept he must hear the morning blessings from someone who has slept. He is allowed to recite the blessing after washing his hands, and having gone to the bathroom.
* For a man who has been awake all night, he must not recite the blessing over the donning of the tzizit.
* In order to be obligated to recite the morning blessings one must have slept at least 30 minutes in the night.
One should stand from the beginning of the Aliyah (portion) that contains the 10 commandments.
Customs of Shavout:
It is the anniversary of David Hamelech’s death- therefore there is a special merit to say the whole book of Tehillim during the day of Shavout.
The Torah is compared to Milk and Honey- therefore on Shavout many people have the custom of eating diary as a physical manifestations of this idea.
One is allowed to decorate their houses, and houses of worship with greenery to commemorate Mt. Sinai which was surrounded by greenery at the time of the giving of the Torah.