Brand new to substance painter, ffbx isn't importing properly. Please help!

Hi

If you do not have UVs in the fbx you generate in Blender. Use Auto UV unwrap in Painter
https://substance3d.adobe.com/documentation/spdoc/automatic-uv-unwrapping-188974350.html
In Painter check the option Auto UV unwrap in the new project window and in the options (click options), make sure to have Recompute all) and if you have UVs then use "Generate only missing data" then Auto UV unwrap will only compute what is missing.
In Blender, to generate UVs, go to "UV Editing" mode, then in Object Mode select the objet, "Select > all" then on the left UV viewport  you shoud see the UVs, other wise "UV > Unwrap", then save export in fbx. You can manually modifiy them, and if you want to export several to several Texture Sets, then Assign a different material to each part.

Hope this is useful