⚠️ Warning: This article is not about publishing wallpapers! To publish a wallpaper, just click Steam -> Share Wallpaper in the Workshop, that's all you need.
If you want to create an asset for others to re-use in their wallpapers, you first have to enable the asset creation options in the editor. These are hidden by default to avoid that they confuse new users when trying to publish a wallpaper.
Enable Asset Creation[]
You can enable asset creation and sharing in the view menu by clicking Enable Asset Creation.
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There will now be a new share option right above the wallpaper share option in the Steam menu. Use Share Assets on Workshop to upload your assets.
You can choose between layers and effects. If you decide to share layers, you can select multiple layers from your current project that will be uploaded - including any dependencies they have to internal assets, like textures, shaders, child particles etc. Just make sure you select all layers that you want to share.
If you decide to share an effect, you can choose a single of your custom effects. Unless you already created a new effect, this menu will be empty.
If you're sharing multiple layers, you can share them as an asset pack. This option will allow the user to only import one of those layers into their wallpaper and not all at once. This is useful if you want to create a bunch of similar particle effects, for example, but the user is expected to only import one or a few of them and not all together.
Create New Effect[]
Enabling asset sharing will also enable a new option in the effect menu in the bottom left. You can click on New to create a new shader effect and you will get started off with a basic passthrough shader that doesn't do anything special.
Alternatively, you can first click on any existing effect and then the button will change to Duplicate. That allows you to create a copy of an existing effect and make changes to this - saving you a ton of work. If you want to make changes to an existing effect, this makes it a lot easier to create a variation of one.
Check out Shader tutorial desaturation to get started on a new effect!