We've gotten a lot of questions about how cooking and publishing work in UT3. If you're looking to create a new map and play it in the game (offline or online) this should help get you started:
Publishing and Cooking UT3 Community Maps
The CookedPC naming convention may seem confusing, but it’s a relatively simple process once everything is set up properly. “Cooking” bakes out unnecessary content from the map file, creates the shader cache information needed to properly load and run your map, and improves performance and loading times. “Publishing” sets up the files for distribution and puts everything into the proper directory so that other people can play what you’ve created.
Regarding the Published and Unpublished behavior:
Maps that are saved in the game editor are written to the Unpublished directory by default. This is the working directory for mod authors, and can be found here:
…\Documents and Settings\<UserID>\My Documents\My Games\Unreal Tournament 3\UTGame\Unpublished\CookedPC\CustomMaps
By default, however, the game recognizes only the Published directory when loading content. If you want to test Unpublished content, you can add the -useunpublished flag to the commandline. (The expected mod workflow is to iterate development on levels and content and run the game with -useunpublished.) When a map is ready, a final Publish will write cooked content to the Published directory, and these loading-optimized files will be ready for distribution.
The Published directory is located here:
…\Documents and Settings\<UserID>\My Documents\My Games\Unreal Tournament 3\UTGame\Published\CookedPC\CustomMaps
Saving a game in the editor should create the Unpublished folders. Publishing a file should create the Published folder. If either of those directories don’t exist, you’ll need to create them manually. When you download a map and want to play it, put it in the Published folder and it will then be recognized by the game and appear in the in menus. Note that files that are not in the proper directory will not be recognized by the game and will not load properly or appear in the menus.
I'll try to update this thread as necessary with new / relevant information.