If you have a tree, it will have branches (unless you cut them ofcourse). Law is just like a tree. A look at sociological explanation is really helpful. It beautifully illustrates the process which culminates into law. It starts with the actions of Ego (individual), turns to an habit, then to folkways, mores, customs and finally laws. [click here for wiki says about this.]
But then it does not stop at that. It moves on to develop and grow into a full fledged system of its own. And this is where the tree analogy comes to play. It develops into a discipline with specialized fields and thus its branches. Another process of evolution and we have sub-sets and super-sub-sets and so we have super-specialized disciplines. And so has law witnessed the huge architectural build-up that it has gone too heavy and vast to know it full. So let us start with the ground basics
I hope I don't need to explain what law is or why law is. So let us start straight with its branches. The most prominent of them are; criminal law; commercial law; contractual law; property law; constitutional law; taxation (how could I miss that???) and tort law. Then there are the less prominent ones; armed-forces law; administrative law (generally seen as a part of constitutional law itself); cyber law; space law; intellectual property law; immigration law; child law; juvenile law; family law; disabilities law; racialism law; and what not ...
Many of these are specialized disciples already while some are toddlers, yet to find a proper space for themselves.
At this point I thought I would elaborate the areas I have enumerated above but then if would have been too boring to browse through (though I would have been even more bored writing it up). So I dropped the idea. Any ways, the thing is that this is just an area for specialization and super-specialization. Does not much has to do with a lay-man understanding of the law, for the principles and structures behind each significantly remain the same, except where the special needs and complexities dominate to make specific rules dealing with specific situations. For example, the concept lies writ large at the heart of family law that individuals are free in the decision of their life-partners. But the certain societies wonder that it would be in their better interests (I fail to see how) if only the heterosexuals are permitted to form a union.
So this is how law structures itself. At the centre lies a tree, marking the evolution of law from mother nature (and therefore the intrinsic and constant connection with society) which is the source of all principles and aspirations for growth and then we have specific branches, which deal with different areas of law; More complex the society, more specialized the law, like cyber law, space law etc.
But then this categorization into branches is artificial as in any given situation there can be a cross-section of various issues that may apply. They inter-mingle and apply as a host of problems (so you hire a lawyer) which are to be addressed simultaneously (so the lawyer makes a team of lawyers for the problem) and then convince the judge (both legally as well as extra-legally) that your side is the best one and justice (if at all it exists in this world) can only be served by ruling in your favour ...