Look for a post with a heading like this in the photography forum: ***Submissions for the January photo contest*** That's where you post your entry.

This month's submission thread is here: https://www.democraticunderground.com/1036125313

The post in GD is just an announcement to let people who don't follow this forum know about the contest. Hope this helps!

I always look in culture forms under photography. Then I watch for info on photography contest submissions are open.

for the current contest. Submissions are still open. The host of the current contest will post a link in the Photography forum containing the preliminary threads once they are posted in GD.
The preliminary threads are sometimes hard to find in GD when they are running because it takes people posting responses to keep them near the top of GD. That's why I often just come to the Photog forum to find the links, rather than scroll through GD.