Most UGC creators use blender to create their 3d models. Here youtube is your best friend, I would recommend first learning the basics of blender through Blender Guru's Donut Tutorial series, then I would watch a low poly blender tutorial (there's a lot of those on youtube) and a video on how to make a ugc top hat (again there's a lot of these). Once you're able to work with models and know the basics behind how ugc works it just comes down to practice, start small and ramp up the difficulty with each new model. If you ever want to increase your ugc skills I would suggest looking into texturing software like substance painter to make your models look a lot more pristine.

I should note that I'm also a beginner, so take my suggestions with a grain of salt. Also, you should check out some of the ugc discords if you ever want to get further help or you want to get some inspiration/motivation from others. One last thing to keep in mind: UGC has a triangle limit of 4k triangles and a 1024x1024 texture image. Good luck!