Shavuot commemorates the time of the barley harvest in Ancient Israel. It is also regarded as the anniversary of the moment when the Israelites received the Ten Commandments at Mount Sinai.
Beginning on the day after Pesach, seven weeks are counted. This period is known as the Omer. The fiftieth day, at the end of this period, is Shavuot, therefore, it tends to occur in June.
The eve of Shavuot is an opportunity for study. Many Jewish communities and institutions organise study session that last long into the night, sometimes even until morning. The festival services include a reading of the Ten Commandments, and synagogues are often decorated with flowers.
As with other biblically based festivals, Liberal Jews observe only one day.
A tradition has developed for dairy foods to be eaten on Shavuot. The explanation for this is that prior to receiving the Torah, the Israelites did not know the Jewish dietary laws about the separation of milk and meat. Therefore only dairy foods are eaten at this festival. That tends to translate as cheesecake!