Rotate the whole thing?
You just rotate the root bone.
Rotate parts? You just add a modify bone node with an exposed rotator pin.
Forward kinematics isn’t a thing, it’s just how stuff works Normally - so its not hidden or complex, it just works like that out of the box.
IK is taking an end point and calculating where the rest of the bones have to be to allow for that position - while taking into account limits so as not to distort the skeleton.
This is applicable to humanoids and organics which are prone to unnatural movements.
When making robots and such its a non issue since you can move articulations pretty much any way you want without it looking bad - maybe with the exception of self collision being needed.
Explain what your end goal is, with examples, you’ll get better answers.