What you want to do is update the text property of the label, when the var point changes value. This is very easy to do with setters and getters (I recommend you read on them since they are super useful). Lets use a setter on the var point, which triggers stuff when it changes value. First you do this:
var point = 0 setget set_point
where setget is a keyword and set_point is just the name of the setter function you will define later, like this:
func set_point(value) -> void:
point=value
$Label.text=str(value)
And you are done! just remember that setters only trigger when another script modifies the value of point, and if you are modifying it in this same script just use self.point = new_value, to trigger the setter