>>272473040
1. Find a good model on bowlroll or something
2. Download it, put it in blender, run CATS
3. Fix whatever else goes wrong
4. Upload it to VRChat with the SDK in Unity

Obviously other players get the data to display the model from VRChat's servers when they see it in game. There's in game features to share models so other people can use them as their own avatars too. There's ways to rip avatars without permission but that's illegal and rude.