You may have noticed quite a few new years festivals at this time of year, but not exactly on December 31st and January 1st. For a long time, no one agreed on what calendar to use (and in fact many religions use different calendars than the Gregorian one), but people, including farmers and early astronomers, noted the passage of time by the moon and the stars.

For Mahayana Buddhists, today is the New Year, the first full moon of January. There are other Buddhist new years (Tibetan Buddhists celebrate at the end of this month).

What do Mahayana Buddhists believe?

that any person can potentially achieve Buddhahood, which is when you ascend to the ultimate reality (nirvana);
that Siddhartha Gautama was one incarnation of the Buddha;
that negative mental states must be worked through (karma);
that evil is a result of cravings, attachments, and ignorance; and
that life is suffering, but that intense suffering may lead one to achieve nirvana sooner.