So, you want to create something?That's nice, but here's the deal.
Before you (we) get started, you should have (or download) some assets to work with (obviously), and probably an application to help you preform that (Photoshop is the best choice, for instance) and something to convert audio and fonts.

Before we start, these files are supported: png, ogg, ttf.
For internal info - ini.
To give a life to your future creation you have to create a folder and name it somehow (Preferably without additional symbols to avoid system's missinterpretetion).
You will have to put assets in this very folder, here the list what must be there:

.png format (Background, info, characters and objects)
• background (580x460) - This is what will be behind any menu or game screen
  
• border (580x460) - That's a game field, center of which must be colorless with 'walls'
  
• menu (580x460) - Startup screen in a nutshell
  
• preview (580x460) - Your creation logo in-game and on Steam Workshop page
  
• message (300x160) - Information screen on which text will appear
  
• menu_select (16x16) - An arrow which select certain option on screen
  ----------------------------------------------------------------------------------------------------------------------------
  
• cube1 - cube6 (32x16) - Character assets.
  
• enemy (32x16) - Enemy asset.
  
• slime (16x16) - Movement skipper, gross!
  
• door (32x16) - An interactive oblect asset.
  
• trapdoor (16x16) - WALLS ARE COLLAPSING BEHIND YOU! Makes floor a single wall.
  
• wall (16x16) - World's a box, wall it's gradient, huh. Static wall.
  
• box (16x16) - Pushable friend, right, GLaDOS? You can move this around.
  
• button (16x16) - Pressable object, nuff said. Use it to acess something.
  
• clearzone (16x16) - Congratulations, you're WinRar. End to which cubes must be guided.
  
• ice (16x16) - WeeEEE!!....oh, it's floor again. Makes you move until next stable surface.
  
• invbut (16x16) - Invert arrows, 'move barrels'.
  
• invert (16x16) - Your controller is inverted, deal with it.
  
• killall (16x16) - DOOOM! Destroy all enemies.
  
• safe (16x16) - Normies, GET OUUUT. Enemies cannot enter this area.
  
• path (64x16) - Moves you in one direction. Fancy.

.ogg format
• music - This will be playing from any point in the game, so choose wisely ;)
  
• sound_win - This plays upon copmleting the level (Should be around 2-3 seconds long)
  
• sound_lose - This plays upon character's death (Approximately for 3-4 seconds)

.ttf format
• font - Obviously, this is how in-game text will be lookin'. Try not to pick something shabby.

After finishing putting files (or downloading template, heh), we should tell the game, this folder we're using now our skin. How you might ask?
By creating .ini file, of course!
Here's how it looks (On 'Template's' example):

A quick explanation:
• WorkshopID - Your future Steam Workshop ID AFTER! publishing it in-game, fills in automatically (non-existent if you creating design for the first time)
  
• Title - Name of project, that will be displayed in-game and on Steam Workshop page. Fill it in carefully, it's pretty nasty to fix easily.
  
• Author - Creator's name in-game.
  
• Description - Write anything you want! (CHECK INFO BELOW IN FAQ SECTION HOW TO MAKE SPACES INSIDE .ini!)

Settings section is based on in-game parameters, so it's better to leave them be.

You've got something to create with and got a slight idea of content (I hope, i really do).
Now, let's talk about pictures structure.
As you could've seen, they have different size, it means working with them would be diffierent.

• 
  Characters, Enemies and door have 32x16 image size - one side for active condition, another for 'inactive'. Putting two pictures inside side by side will make change condition, based on their action - etc. open door / clear level / enemy movement.
  
• 
  As for 16x16 files, they require only one image inside them, 'cause they're static.
  
• 
  Arrows (or path) require 4 different images beacause of it's 64x16 resolution to imitate directions.

This section is reserved for any questions about content making.