In your Dashboard go to My Mods and fill out the Mod Creator Application.
Wait for your application to be approved.
If your application is not found satisfactory, then an response on what you need to add will be made to it instead, you should therefor check back on that page often until your application is approved.
Once approved, you should now have the option Add New Mod. Click that and fill out the mod form.
After you have completed the new mod form you will be taken to an edit page where you can fill out the rest of the details and upload files for your mod.
Add the UpdateURL provided to you from the edit page to your mod's config code.
Fill out as much detail as possible and ensure everything is correct.
Ensure that your mod works correctly.
Upload your mod or provide a direct download link to it.
Wait for your mod to be approved by a moderator.
A moderator may respond to your mod instead of approving it due to your page missing something or needing corrections. You should therefor check back on your mod now and then.
Once a moderator approves your mod, it is automatically listed on the website.
Note that any subsequent changes you make to your mod after it has been publicly listed will also need moderator approval.