How do you celebrate Simchat Torah?
I always encourage people to use Wikipedia and Jewfaq, which do a pretty good job of describing Jewish holidays and concepts. Chabad.org too:
This is not a biblical mandate, right? But a traditional one celebrating when Torah was given and I believe you start it over with Beresheet, right?
No and yes:-) The traditional dating puts the giving of the Torah at Shavuot, the festival of Weeks/Pentecost. (I say traditional because the actual date of the Giving of the Torah at Sinai can only be inferred from the text and is not explicit.) But the universal tradition today is to read 1/52 of the Torah every week starting the Shabbat after Sukkot and finishing on Simchat Torah. When we finish with the portion of Vezot Habracha (This is the Blessing, Deuteronomy 33:1–34:12), we immediately start with the first subportion of Breshit. The Shabbat afterwards we read all seven subportions (aliyot).
Hope this helps!