You can then select the item you want to create a skin for on the left, this will open the workshop item editor.
From here you can now export and view the selected model and by clicking the texture square this will allow you to select a texture off your local system, you can also control lighting and enabled a backdrop for screenshots.
Clicking the small cross in the bottom right corner will reset it back to default or you can simply re-select the item and it will reset all values to default.
You can also control the color tint of the base color and other parameters using a color picker and value slider.
The Texture format is the following
Base Color/Opacity - Color + Alpha Opacity Mask
Normal - Normal
ORM - Ambient Occlusion/Roughness/Metallic
Emissive Color - Emissive Color AKA Glow
Keep the texture power of two, ie, 256x256, 512x512, 1024x1024.
When baking textures in Substance painter the Unreal Engine 4 preset should be used to generate the correct layer format, Texture format should be always TGA.
We also don't allow exporting of current textures for various reasons.