All intellectual property receives automatic copyright status at the moment of creation. You don't need to do a thing to get it. Nevertheless, registration is a good idea as it conveys a number of benefits.
The Meaning of "Copyright"
Copyright is a form of legal protection mandated in both the U.S. Constitution and international courts of law. It protects intellectual property against plagiarism or any other unauthorized use.
"Intellectual property" means, without limitation, any original work authored in any medium. Copyright protects music, films, television shows and books, but it also extends to dance choreography or any other tangible medium. Only at the far edges of definable authorship has doubt ever existed. Even then, intellectual property creators have usually prevailed in suits over copyright protection for such things as furniture and cell phone designs.
How Copyright is Obtained
The U.S. government maintains a copyright office where you can register any intellectual property. This sometimes leads to a misunderstanding by persons unfamiliar with copyright law, who may believe that if a work is unregistered, it remains unprotected.
In reality, your original work has copyright protection from the moment of creation – this protection is clearly stated in copyright law. You don't need to do anything to obtain it. Copyright registration does have several advantages, however. It publishes your protection widely and, in some instances, helps establish which author created a particular work first. In addition, it may also entitle you as the copyright holder to statutory damages and other fees in a suit to protect your interests. Think of it as a deterrent.
The Meaning of Fair Use
In the U.S, copyright law has a "fair use" exception that many other countries – Great Britain, for example – do not recognize. Like the copyright protections of unregistered works, the meaning of fair use is widely misconstrued. One common misunderstanding, for example, is that another author, not the original copyright holder, may sample up to 30 seconds of a song without obtaining a right to use. Such a sample violates copyright law, and so does a one-second sample.
There is no exception based on brevity. You can probably sample a single bass drum hit because it's hard to identify where it came from. Sampling the phrase "school girl" without getting permission first, however, would undoubtedly get you in a lot of trouble with the able copyright attorneys protecting Chuck Berry's estate.
As the fair use doctrine has evolved, it allows very limited uses of copyrighted material in two environments. When the second author is unlikely to obtain a financial benefit or the original author is unlikely to be deprived of income, brief quotes are generally allowed. A music critic writing about Bob Dylan's imagery, for example, can likely quote brief excerpts from Dylan's songs. A music critic publishing an entire book of brief quotes from Dylan's songs would almost certainly need to obtain permission.
The other exception is for parody. Alec Baldwin can quote President Trump's speeches on Saturday Night Live for comedic effect. You can't publish the same speeches in a book you're selling because you're serious.
The Meaning of "All Rights Reserved"
The meaning of the phrase is self-evident, but it has no practical application because the default right for any copyrighted work is that all use rights are reserved to the copyright holder anyway, whether specified or not. The phrase remains in use mainly because a 1910 version of international copyright law mandated it. Subsequent revisions have made its use unnecessary. There's nothing wrong with attaching it to a copyright notice, but it has no effect.