Answer: If you want to officially copyright your work you can go to the Library of Congress website (www.loc.gov), find the copyright resources from their home page and proceed to go through the forms and processes provided by the website to officially copyright your work. Word of caution, this costs a bit of a money for a starving writer. There's also a lot of legalese you'll have to translate to determine which forms you'll need, to fill them out, etc.
A private lawyer or an online legal service (like LegalZoom.com) can help you sort through the muck. This will cost more money.
If you are planning on self publishing, then officially copyrighting your work with the Library of Congress may be a good plan for you.
However you should note, in cases where you are trying for traditional publishing, copyright laws protect even those who do not pay to have their work cataloged by the Library of Congress.
The minute you create something, a poem, a song, a short story, an article, etc. you own the copyright to it. If having that official copyright notice in your hand will give you the peace of mind you need, then it is worth its expense. But in most cases, copyrighting every piece of work you write is just a waste of time and money. Writers are proud of their work and are naturally protective of it, afraid that someone is waiting around the corner to steal their work. But the truth is, manuscript theft just isn't that prevalent. And even if your work does get stolen, you are still protected under copyright law, regardless if it is registered with the Library of Congress or not. You still have all the rights to take legal action against the person who stole it.
In the meantime, if you are trying for traditional publishing, focus that time and energy into submitting your work to agents, producers, and editors. Then if your work is accepted, they will take care of officially copyrighting your material.
Peace and prioritizing,