SnG means Sit-and-Go. Those are tournaments that starts as soon as they are full. There are single-tables and multi-tables. They play just like a usual tourney, with rising blinds and such. On a 10 person SnG, usually the top 3 places gets paid.

Read http://www.flopturnriver.com/phpBB2/...pic.php?t=8202 for a very nice and detailed guide by DavSimon!