It’s not easy to find a simple online explanation of the difference between Official and Unofficial sources of law. My explanation may fill in that gap – or not, depending on your specific question. (And a blog post this long can hardly be called “simple,” but such is life — and law.)
1) In a nutshell, an official source is a source that has been authorized by an official body, such as a court or a legislature. In Oregon, for example, we have the official statutes of Oregon, published in the Oregon Revised Statutes (ORS), by the Oregon Legislature, through Legislative Counsel. (This official statutory compilation should not be confused with Oregon Laws, which is the official session law compilation.)
2) We also have in Oregon, as do many states, an unofficial statutory compilation, the Oregon Revised Statutes Annotated, which is published by Thomson-Reuters (West Group).