I will attempt to illustrate the 2 most common causes of back pain from doing the deadlift, seen from the novice to intermediate levels. Most commonly, you are experiencing pain due to having tissues being compressed. The compressed tissue is either the lumbar discs or the paddings of the joints (E.X. SI joint & facet joints). At other times, you can have pain from tissues being over-stretched, and in this case, it is either your muscles or ligaments being over-stretched.
For illustrative purposes, curl your index finger and sit on it. This is the equivalent of joint compression under flexion. Tissues between your finger joints (the cartilagenous padding) get irritated and cause pain, followed by inflammation if you irritate it enough. The same concept can be applied to the lower back. Thus, you can also imagine how over-stretching can occur in similiar fashion by hyper-extending your fingers.
Each of these two injuries can be severely debilitating and can take you out of the gym for weeks. At worst, it can even cause permanent disabilities.
Compression and over-stretch injuries from deadlifting happen often, and these injuries can be narrowed down to 2 major causes:
1. Core pressure provides straightness and rigidity to the lower back. This cannot be stressed enough. You need to learn how to produce maximum core pressure, so that you can hip hinge. If you are unfamiliar with core pressure (or bracing at the core), then you won't be able to hip hinge. If you can't hip hinge, you shouldn't deadlift.
2. Hip hinging allows you to exert maximum strength and lift from the gluteus maximus and the hamstring muscles. You never want to lift from the lumbar erector muscles. That is not a deadlift. If you cannot hip hinge properly, stop deadlifting.
How to brace at the core:
How to hip hinge:
So to sum up the article, start by learning to brace at the core, and then learn to hip hinge properly. By the time you are proficient with these two techniques, you can then begin deadlifting safely.