You can use any 3D modeling software to create content for VRChat. A popular and free software is Blender. To get a 3D model or avatar into Blender, all you need is a 3D file type, usually an fbx. Importing an fbx object into Blender will allow you to edit that 3D file. Exporting the fbx object will update the file and let you upload to VRChat. An avatar fbx object will include information for rigging. You’ll be able to see the bones and blend shapes in Blender.
Import an FBX file into Blender
To import an fbx object, open Blender. In the top left corner, go to file -> import -> FBX.
Navigate to the saved file on your computer.
People are usually referring to avatars when referencing Blender and VRChat. A lot of tools have been created to help players easily create avatars in Blender. If you are trying to edit an avatar, you should import the Cats Blender Plugin for VRChat. This plugin will help you rig your model, create visemes, and set up eye tracking for VRChat. There are also a ton of tutorials on Youtube showing how to use the plugin. A lot of the older tutorials are still relevant, just make sure you are using the current VRChat SDK and Unity version.
Import a Plugin into Blender
Download the Cats Blender Plugin. It should be a zip file on your PC.
Open Blender. In the top left of the program go to edit -> preferences.
In preferences, go to add-ons and then “Install…”, in the top right.
Navigate to the zip file containing the plugin and select it.