Technique is important for the deadlift. My personal experience is that it is too easy to add weights and once you get above your body weight, small errors increase the chance of back injuries.
For the correct posture and technique, see this OP Physcial Fitness: What is the correct form for deadlift? and this two videos: Deadlift set-up and Deadlift back angle
Deadlift is an excellent exercise for the whole "Posterior chain" (i.e. the whole system of back, glutes and legs), see picture below.
I find it easier to understand it in terms of the wholeness instead of individual muscles. So, it is not an exercise only for the legs or the back which is why you sometimes see people having problems with fitting it in a "upper body" and "lower body" workout routine.
Whether you should wear a belt or not seems to be a hot topic of debate, see Google: belt or no belt deadlift and Dead lift - belt or no belt. It seems to boil down to "depends on.." where ".." relates to your specific context (age, skills, goals..).
Personally, I don't use a belt since it is one more item to bring to the gym and if you have to lift something heavy off the floor in real life, the belt will not be there.