I'm new to D&D and I don't understand all of its concepts, for example, Astral Plane.

From what I understand, you can travel there physically through a portal and travel to other planes this way. However, you can also use a spell like Astral Projection. This spell transfers your consciousness to the Astral Plane and connects it to your physical body with a silver cord. Your body stays where it was and if the cord is broken, you die.

What happens when this Astral form enters a portal to another plane?