Here’s a good video that will help explain.
Crow and Crane!
Crow is the beginner one. The knees are lower on the arm as you balance. Your arms are bent. Your center of gravity is lower to the ground so it’s easier to hold.
Crane is more advanced. Your knees are basically in the armpits. Your arms are straight so your center of gravity is a lot higher … and it’s harder to hold the balance.
But with both poses, it’s all about finding your center!