I GOT IT! I leave it here in case someone else wants to go a little beyond the tutorial
1- Firts, create a variable at startup and declare it false
var is_dead = false
2.- Declare it at the beginning of func process(delta): as a false condition, so that it is alive and can move (and move the rest of the _process → to be inside of "if isdead == false"
func process(delta):
....... if is dead == false:
.............. var velocity = Vector2()
.............. if Input.isactionpressed("uiright"):
.............. velocity.x += 1
etc etc... etc...
3.- Add this lines at func onPlayerbodyentered(_body): that specifies what to do when the players dies:
func onPlayerbodyentered(body):
....... var velocity = Vector2() #to call states of movements #NEW
....... isdead = true #to declare that... is not live... duh #NEW
....... velocity = Vector2(0, 0) #to make him stop #NEW
....... $CollisionShape2D.setdeferred("disabled", true)
....... emitsignal("hit")
....... $AnimatedSprite.play("death") #to play your animated sprite for death for the player #NEW
....... yield($AnimatedSprite, "animation_finished") #to hold the next "hide" until the death animation is finished #NEW
....... hide()
4.- Make him life again at the beginning of the function start:
func start(pos):
....... is_dead = false #New
....... position = pos
....... show()
....... $CollisionShape2D.disabled = false