Hello Snaffer, and welcome to the N forums.
There is currently no way to create episodes for the game, however you can:
-Submit them to numa, the N user map archive:
http://nmaps.net/
You will need an account to submit maps. In order to get an account on NUMA, download N, run it, click on 'configure', enter a username and password in the boxes provided, and click 'create new user'. You can then use that account to log into NUMA.
-Submit them to these forums as a map pack
You're already in the right section for this ;)
Just place your levels in a text file, make a new thread and upload the text file. Once you've done this, most people will know how to download and play your maps.
-Place them in your userlevels file, so that you are able to access and play them easily
Find the userlevels.txt that should in the same folder where you keep N. If it doesn't exist, simply create a new text file in notepad called "userlevels" and save it to the N folder. Open up the text file and write this at the top "&userdata=" (without the speech marks).
You can then paste the map data for your levels beneath that, and you will be able to play them in-game by clicking on the "userlevels" button on the main menu screen.
Make sure that your maps are pasted into the text file in this format:
$map name#author#type#map data#
Place the map data where i've written "map data". Don't forget the final '#' at the end.
I think that's all, shout out if you have any problems at any stage.