Check out example codes for "drag sprte godot". It will help you in understanding the concepts better.

Code Example 1

extends KinematicBody2D

# Pickable needs to be selected from the inspector

var can_grab = false
var grabbed_offset = Vector2()

func _input_event(viewport, event, shape_idx):
    if event is InputEventMouseButton:
        can_grab = event.pressed
        grabbed_offset = position - get_global_mouse_position()

func _process(delta):
    if Input.is_mouse_button_pressed(BUTTON_LEFT) and can_grab:
        position = get_global_mouse_position() + grabbed_offset

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