How do I understand the law behind the procedures I follow?

You follow procedure faithfully, but you can feel the gap: you do not fully grasp the law underneath it, and you worry that one day that gap will cost a case. That worry is to your credit. It means you want to protect the work, not just perform the steps. Procedures are the surface of something deeper. Each one exists to protect a principle, a right, a piece of fairness the law is trying to guard. When you know only the step and not the reason, you can follow it correctly and still miss when it truly matters, or why. Learning the why is what turns a rule-follower into someone who can protect a case. Pick one procedure you use often and go find out what it is actually protecting, ask a lawyer, read the reasoning behind it, follow one rule down to its root. Do that a few times and the whole system starts to make sense, not as a list to obey but as a logic you understand. That understanding is what keeps you from compromising the thing you are trying to protect.