UGC is the abbreviation of User Generated Content. Basically, it's anything out of the game (mostly pictures, words, video shots, dubbings) that a player can upload into the game for other players to share with.
If you already have an accomplished template, you can opt for the template from images below the new button. These images shown will be jpg images in your custom folder (For example D:\Nexon\Library\maplestory2\appdata\Custom\Equip). You can open your folder including all the images by clicking on the open folder button:
You can also relocate jpg images to this folder and they will show up in the Maple Workshop after you close and start over.
You can also create a new template. If you do, it should create a new file and open up a default image editor (Paint for example). You can from there copy the image and paste it onto a better image editing software, such as Paint.NET, Paint Tool SAI, or Photoshop. I personally use Paint.NET. You can, of course, use regular Paint, but it will be extremely difficult because there is no layer functionality in such a basic image editor.
Make sure that if you are copying and pasting the template onto another image editing software that you save it into the folder that contains the images.
Once you have saved it into your folder or replaced the original template, any changes that you make to this image will immediately show up in the preview in the Maple Workshop. For example, if my character was previewing template_1535290684.jpg, I can change the template from this:
and saving it will change my character preview from this:
This automatic update of the preview is extremely helpful because you will make many changes to the template and will want to see if your edits line up since two opposite sides of the template will wrap around.
For general tips on the actual designing of the UGC, I don’t really have much to offer personally, since I am not an artist, nor do I have a tablet. It’s probably a good idea to use reference pictures of actual clothing online, or if you’re basing your character off of some anime character (like me) or character from a movie, you can design your clothes off of them as well.
I use Paint.NET and utilize a ton of layers when making a new piece of clothing, as well as several plugins for Paint.NET, including the Smudge tool, Drop Shadow, Feather, Inner Shadow, and Object Shadow.