kuligs2
More info on basic AnimationTree tutorial
Animation StateMachine node with conditions. I haven't used this node much before but it looks powerful.
That should help you to get started. The first step is setting up your character to a rig and animate them before import to godot. Since you plan to use rigify I can't help much (I make my own simpler rig), but tutorials should be widely available.
One thing I'd point out is take care on how you use parameters in code.
eg. AnimationNode:
Transition
$AnimationTree.set("parameters/Transition/transition_request", "floor")
Blend2
$AnimationTree.set("parameters/Blend2/blend_amount", 1)
BlendSpace1D
$AnimationTree.set("parameters/BlendSpace1D/blend_position",1.0)
I always get confused when to use blend_amount or blend_position 😅