The second six on six newbie mix cup is about to be begin with the special moniker, Christmas Cup. The rules are simple; its a double knockout tournament where teams are comprised of five individuals and one experienced mentor, who will then take part in a week long tournament with some great christmas prizes.
No prior TF2 experience is required, although they reccomend you take part in a few matches beforehand to get a feel for it. These can be joined via their Steam community. You can also seek out a mentor via the same source.
To sign up, or see additional rules, visit their Steam community group.