>>336116986
https://www.youtube.com/watch?v=AxnjgvWyqQI
This tutorial on the basics of 3.0 from when it released are still mostly applicable. Watch the entire tutorial series first to get a rough idea of how 3.0 works then look up any specific questions you have. Worst case ask here: as long as you're willing to learn people here are willing to help.

For your specific questions: Any animations you want on the avatar (hand gestures are the main one if you're non-index) you need to have set up already. If you want to set up a toggle, you need an animation for when the toggle is enabled.
You will need to make VRC menus and parameter lists, and animators (FX for expressions, Gesture for hand gestures).