When you have your map ready, just create a post, say whatever you like and ATTACH the map to the post.
The size limit for an attachment is 50 Megs.
This attachment should be a ZIP archive that contains:
- the map UNR (named "yourMapName.unr")
- a screenshot JPG (named "yourMapName.jpg")
- a README text file (named "yourMapName.txt")
- any packages needed by the map (such as UMX, UTX, UAX, U, etc)
Remember the naming convention for contest maps is "DM-XC-YourMapName" (DM, CTF, MH, etc).
Hopefully your map is not bigger than 50 Megs, otherwise you will have to split into two ZIPs etc.
Maps should be submitted up to December 15th midnight are ON-TIME.
Maps submitted after that will be accepted up to December 20th midnight but are deemed LATE.
Late maps will lose 1 point in score (see the RULES in the first post of the contest thread).
At December 20th midnight the contest is CLOSED, and all contest maps will be collected from the thread
and sent for judging... details of the judging phase and voting poll will follow.
So everyone do their best to finish

Final Note: Even if you're just about done but run out of time, just make sure you can play a match in it and wrap it up as-is.
You can always finish it up nice and pretty quickly afterwards as a V2 - there will be map-pack after the contest is judged and voted...
So there will be a short period where some maps could be bug-fixed if neccessary...
Good Luck!