To create the State Machine, simply create a new State Machine Node.

To create a new State, create a script similiar to this...

extends State
class_name STATE_NAME # Your state's name

# Runs when the state is entered
func enter():
    pass

# Runs when the state is exited
func exit():
    pass

# Updates every _process() update (When state is active)
func update():
    pass

# Updates every _physics_process() update (When state is active)
func physics_update():
    pass

To add the State to the State Machine, create a new Node of the State you just made, and add it as a child of the State Machine.

To transition to other States on the State Machine, make sure there are more than one State as a child of the State Machine.

To transition to another State, you can use the Transitioned signal (signal inside State script)...

# (CURRENT_STATE, NEXT_STATE_NAME)
Transitioned.emit(self, "EnemyIdle")

If you need to check if a state is active while inside of the state, for example, inside the EnemyIdle state you are checking the _on_area_entered(): (you might already be getting an 'Cannot change state from a non-active state') you can use the active boolean included inside the State class to check if the state is currently active.

# Instead of doing this...
func area_entered(area):
    # Code here

# Do this...
func area_entered(area):
    if active:
        # Code here

If you have any issues, create an Issue or message me on Discord at itsmealec.