whats the best way to copyright you work?

Copyright is a bundle of rights that are yours AUTOMATICALLY when you create an "original work of authorship" and fix it in a "tangible medium of expression." If you record your song, you have fixed it in a tangible medium of expression and you own the copyright to both the song itself (the abstract song that you can arrange and record in various ways or write out sheet music) and the sound recording you made.

You can pay a fee and register the copyright in your song with the Register of Copyrights at the Library of Congress. This allows you to recover certain types of damages (i.e. "statutory damages") if someone infringes your copyright by making unauthorized copies, recording and selling it without your permission, or performing it publicly without your permission. If you don't register your works, you can't recover statutory damages, so it is in your interest to register your works.

http://www.copyright.gov/eco/

Good luck.

Please see my legal guides on how to register your copyrights, how to protect your songs, and how to monetize your songs.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.

Visit amazon.com, query its books database for "music law" and then again for "songwriting" and buy a few books on the subject. If you're serious about trying to protect your songs and/or to make money from your songwriting then doing some homework on the subject is required. Good luck.