>>279011172
assuming you have a finished model you just want to get into vrchat and it's already in the correct format:

>download unity
>download the vrchat sdk
>start a new unity project
>import the vrchat sdk and the 3d model to your project
>set the model up as a humanoid rig, place it somewhere in your scene
>attach the vrc_avatar_descriptor component
>upload the avatar to the vrchat server

that's the bare minimum