Hi there, glad to have you on board with modding!

We strongly recommend you join our Discord, as there are quite a few people in there that can help you with modding more quickly/easily. Here's a link: Two Point Discord[discord.gg]

If you mean a thumbnail image for the Workshop, you can upload an image as part of the Steam Workshop Upload tool (the one you can either run through Steam, or via the menu option in the Unity project under Tools -> Steam Workshop Upload Tool). If you mean the icon in-game, then you'll need to follow the section of the item modding guide titled "Creating a Sprite Atlas for Icons", the guide can be found here:
Item Modding Guide[docs.google.com]

There currently isn't a super easy way to preview stuff in the Unity editor itself (the easiest way would probably be to just drag your mesh into the scene and apply your material to it). It's best to jump into the game and test it there, we'd strongly recommend starting with the Quick Guides to get a feel for the entire process with something simple and then progressing from there.

All the best,
James

Hey hey,

Thanks for replying!

Yeah I meant the sprite, I found a guide for two point campus and applied that to this.

So far so good but I'm stumped at wallpapers because they show up so dark in game but i'll get there ^.^ Learning as I go and i'll check out modding in discord for help, thanks for that link btw :)