Hey, yes don't hesitate to ask question about a feature. I didn't finish the complete tutorial about this one.
So you have like a chain of bones (several bones in parent-child relation). You select the first bone ( so the first parent bone of the chain not the tip bone)
Then you give it the ik constraint, and you choose a bone to target outside the current chain (you can click on new to be sure). All the other bone should have the default constraint "from parent" else if you put ik it starts a new chain.
And that's it you can move your targeted bone to move your ik bones chain :)