The © or Copyright sign is used to notify other persons or entities that a particular work is copyrighted. Even though any work, once put into a tangible or electronic format to make it available for others to use or consume, is theoretically copyrighted to the author(s), new United States laws concerning whether they are actionable came about because of lawsuits and the action of a judge. Now, in order to be able to sue someone over copyright infringement, one must already have their registered copyright documentation in hand. It used to be that all one had to do was to fill out the form and pay the fee to the government, but now the time between those actions and the issuance of the copyright document (usually four to eight months of lag time), one would not be covered. This is still being dragged around by more lawsuits, and Congress may eventually get involved. This could be a good thing or a bad thing, like the Sonny Bono Copyright Extension Act, aka the Mickey Mouse Copyright Extension Act.
To actually get the little C with a circle:
In HTML, use ©
In Word, just type (c) and it will automatically change it to the correct symbol. This also works for ® (r) and ™ (tm)
Use the Character Map tool to find the symbol and copy/paste it
One must use the symbol © and/or the word Copyright on the work followed by the year it was created. ©2020 for this writeup, for example.
Note that copyright and registered trademark ® and trademark ™ are different animals altogether, although they tend to get confused for each other. Copyrights protect works like novels, magazines, images, and audio recordings. Trademarks are used to denote something is used specifically for a person or organization to indicate that they are the sole legal holder of a signifier that shows something was created by them. Back in the 1700's, silversmiths like Paul Revere would use a special stamp on his silver to indicate it was an original Revere ware. In modern times, people can trademark things like a product name (Velcro™) or the name of a company (Everything2™) or even the look of a brand (Amazon or the smile logo). The registered trademark ® is used to note that the trademark is registered with the federal US government. This is an expensive process and in many cases requires the services of a trademark lawyer.