I have been reading the documentation for monthly tournaments, and I don't understand it. Is there just one monthly tournament per month for each game, or can there be several?
Last year, November I think it was, I entered a GWG monthly tournament, and as it happened I won all my games in the first round/group. Will another round/group start sometime? Or have I missed it by failing to fill in a form somewhere?
It must have been December, as you didn't enter the November one.
The second round should start as soon as all the first-round groups have finished - but most of them (10 out of 19) are still in progress, so this isn't likely to be any time soon.
(Even the October and November second rounds haven't started yet.)
Click on "Tournaments" on the left of this page. Then click on "registrate" for the tournament you want to enter. Suppose for example you register for the next monthly tourney in GWG. It may take a few days for enough people to register, before a tourney starts. Once it starts, return to the Tournaments page and register again. This will put you in the next tournament.