Blender Export Help

This is a good idea for a first mod. The first step to get it into the game would be setting up a correct folder structure. Go to the Unpacked folder in your mods and add a folder with the name of the new mod. Then take a look at how official vehicles and props are set up, and replicate the same structure in your new folder, for example vehicles/donut/. Next export your model as collada (.dae) and put it in that folder. You will need to create materials using the textures you have created, you can base them on the example: https://documentation.beamng.com/modding/materials/vehicle/typicalmaterials/#standard-material Or if you don't have textures but just solid colors, you can use a simpler one: https://documentation.beamng.com/modding/materials/vehicle/typicalmaterials/#single-color-material

The next and hardest step would be Jbeam. If you are ambitious, you can try doing one from scratch, but if you want to do it faster, you can modify the existing Large Tire props as they have a similar shape to your donut. You need to understand how Jbeam works, so I recommend reading the basic pages of documentation:
https://documentation.beamng.com/modding/vehicle/intro_jbeam/
https://documentation.beamng.com/modding/vehicle/intro_jbeam/jbeamsyntax/
https://documentation.beamng.com/modding/vehicle/intro_jbeam/partslotsystem/
https://documentation.beamng.com/modding/vehicle/intro_jbeam/debugtools/
https://documentation.beamng.com/modding/vehicle/intro_jbeam/common_issues/

If something is not clear, and you can't find an answer to your questions in documentation, don't be afraid to ask for help, making Jbeam is a long process so you are not expected to get everything from the start. You can join the Modding For Dummies Discord server, it has many helpful people in it. Good luck with your mod!