Prerequisites: basic crochet terminology, slip knot
To create a slip knot, create a loop, chain through the loop, then pull the loop tight.
But if you don’t pull it tight, that first loop is a valid chain (just make sure to secure the end later)
And if you make the first loop bigger…
It becomes a magic circle :)

FAQ
That’s knot how I do it
It’s based off the tutorial here. The magic circle in that video is exactly the same as the one here.
Can you still close the circle since the tail end is wrapped around the loop
Yes, it’s easy to pull, try it!