Simchat Torah means "Rejoicing in the Torah." This holiday marks the completion of the annual cycle of weekly Torah readings. Each week in synagogue we publicly read a few chapters from the Torah, starting with Genesis Ch. 1 and working our way around to Deuteronomy 34. On Simchat Torah, we read the last Torah portion, then proceed immediately to the first chapter of Genesis, reminding us that the Torah is a circle, and never ends.
This completion of the readings is a time of great celebration. There are processions around the synagogue carrying Torah scrolls and plenty of high-spirited singing and dancing in the synagogue with the Torahs. Drinking is also common during this time; in fact, a traditional source recommends performing the priestly blessing earlier than usual in the service, to make sure the Kohanim are not drunk when the time comes! As many people as possible are given the honor of an aliyah (reciting a blessing over the Torah reading); in fact, even children are called for an aliyah blessing on Simchat Torah. In addition, as many people as possible are given the honour of carrying a Torah scroll in these processions. Children do not carry the scrolls (they are much too heavy!), but often follow the procession around the synagogue, sometimes carrying small toy Torahs (stuffed plush toys or paper scrolls).
Simchat Torah is a holiday on which work is not permitted.
Source: Bard, Mitchell G. Jewish Holidays: Simchat Torah, 1998