The process for uploading new content to the marketplace is pretty simple. Just follow the following few simple steps:
1. Connect via FTP to files.gamedev.net using your Gamedev.net username and password
2. Upload your content packs
3. Create individual marketplace entries by clicking on the "Upload File" button in the marketplace.
4. When you go to select the file just choose "Submit file uploaded to files.gamedev.net (enter filename of file)" option and enter the exact filename of the file you uploaded to our server. Our software will grab that file from your FTP and tuck it away in a secure location with a different filename as well. After the file is moved to our file vault it will no longer exist in your FTP space.
5. Make sure you give your files a few attached images as well as a nice description. That should at least get you started. Let me know if you have additional questions. You control the pricing on your items, but remember that it's only worth what people will pay for it.