Key points of rotation and movement are the key effectors on a object when it’s moving, for example, the anchor points on an arm in an animation would be on the wrist, elbow and shoulder.
Forward kinematics is wen you move each individual effector one at a time.
Inverse kinematics is when if you pull one of the effectors, it will move all at once.
How to create chain
Download chain link brush to photoshop
Create each chain link on their own layer
When you create the first chain link you should rotate the chain link so it’s horizontal this can be done using the shortcut cmd+T and then rotating
Then simply copy and paste that layer 4 times so you have 4 chain link on 4 different layers, a short cut for this is clicking alt on the layer and then dragging.