Basic Astral Projection

You project a part of your body into the Astral Plane (the spell fails and the casting is wasted if you are already on that plane). The material body part you leave behind is unusable but still needs everything it would normally need to survive and can be attacked.

Your astral body part resembles your mortal form in almost every way and hovers in the air. It also replicates your game statistics and possessions that it currently has (if you have a dagger in your mouth and you transport your head, you reatain the item; if your hand is transported with a sword in it, you retain the sword). 

The body part also glows in a color of your choice and has a glowing cord sticking out of it. This cord is your tether to your material body. As long as the tether remains intact, you can find your way home. If the cord is cut-something that can happen only when an effect specifically states that it does-your soul and that body part are separated, sometimes killing you instantly, but always removing that body part from existance.
Your astral form can freely travel through the Astral Plane and can pass through portals there leading to any other plane. If you enter a new plane or return to the plane you were on when casting this spell, your body part and possessions are transported with it. Your astral body part is a separate incarnation and can be controlled by you even across planes. Any damage or other effects that apply to it have no effect on your physical body, nor do they persist when you return to it.

The spell ends for you when you use your action to dismiss it. When the spell ends, the affected body part returns to its physical body, and it can be used again.

The spell might also end early for you. A successful dispel magic spell used against an astral or physical body ends the spell for that creature. If a creature's original body or its astral body part drops to 0 hit points, the spell ends for that creature. If the spell ends and the cord is intact, the cord pulls the creature's astral form back to its body part, ending its state of suspended animation.