Most people acquire copyrights every day. Your social media posts, for example, are copyrighted to you automatically. The user agreements you clicked on without reading gave the social media outlet permission to repost your copyrighted work within the software.
Your letters, texts, assignments, photos, videos, etc. are all automatically copyrighted to you.
Every time you create something (in a fixed form), you have created new content, and that content is covered by copyright protection in the United States. This is automatic. You don't have to do anything. You already hold the copyright.
Examples of works covered by copyright:
Note: Copyright protection applies to original works that are fixed in a tangible medium of expression.
Copyright is actually a bundle of rights. These rights include rights reserved to the owner as follows:
Because these rights are imagined as a bundle, the owner of the copyright can give away, sell, or otherwise license some or all of these rights to others (e.g., when an author negotiates a contract, s/he may give the publisher the right to copy and distribute the work but not to make future derivative works, for instance).
Fair use is the flexible, dynamic exception to copyright law that serves to balance the rights of creators with the public interest in using copyrighted works to advance education, to comment and criticize, and to make new creative content. Its flexibility is often somewhat intimidating or frightening because, when considering fair use, it is very rare to know for certain that a use is fair. It's far easier to determine what is more or less likely to be fair.
It can also be frustrating that the law does not give any clear answers regarding specific amounts we can use to be sure that we are "safe." Fortunately, there are ways of understanding the purpose and function of fair use that can help you feel more confident about usage evaluation and to appreciate the flexibility of fair use.