You can connect it from the Node panel (or in code with connect()) to a method of your script and it will be called whenever a body enters the area.
Thank you. I followed the tutorial from here which is very long to read. Mostly I created an Area2D node, then added a subnode “CollisionShape2D”, and I adjusted the shape within the area I want to take care of in the scene file ( say “my_scene.xml”) .