Copyright Law is part of Intellectual Property Law. In essence, if you create anything, it can be a work of art like a sculpture or piece of music, or something written such as an article, blog entry, science-fiction novel or work in another genre, whether fiction or non-fiction, you own that work. In other words, you own the copyright in the thing you created and no one except you has the right to claim the work as their own or, usually more importantly, the right to profit from the sale of the work.
Other examples of things the creator owns the copyright in are source code (i.e., software, although this once can get tricky), cartoons, videos and other forms of visual expression. You do not have to take any special steps to claim copyright in something you created although you will often see the © symbol which lets you know that somebody claims ownership of whatever it is you are reading, looking at, or experiencing.
Here is a simple example of how Copyright Law works. The owner of this Law Directory hired someone to write this description of Copyright Law. Although this summary does not contain information that cannot be found in other places, the particular order in which the ideas are expressed and the specific words used to express those ideas is an example of a creative work that is most likely copyrightable. A key point is that even though the author of this summary is being paid for doing the work, he (as it happens) is still the owner of the copyright. However, and this is why copyrights are valuable, he is able to transfer ownership of the copyright to the owner of this Directory and it is with that transfer, as long as the owner of the Directory understands Copyright Law, that he is entitled to be paid.
If you create something you want to share with the world and you want to be paid for doing so, before signing any sort of contract for the sale of your work, you must consult with a Copyright Lawyer. There are ways to make money from a copyrighted work that does not require you to sell it outright. You may be able to license the work, which means you, in effect, let somebody borrow and use it for a period of time after which it returns to you and, if things go your way, you can license it again and again and earn royalties for many years (although not forever because after a period many years, copyrights expire. At that point, the work of creative expression is considered to be in the “public domain.”)
The other situations in which you will need a copyright lawyer are (1) if you discover somebody is passing something you created off as their own and are making money from it, or (2) you entered into a contract to sell or license something you own the copyright in and the other party fails to meet its promise to you what was agreed.