You can read the whole "Copyright Basics" FAQ here:
http://www.loc.gov/copyright/circs/circ1.html

Here are a few links to specific questions:

What is copyright?
http://www.loc.gov/copyright/circs/circ1.html#wci

Who can claim a copyright?
http://www.loc.gov/copyright/circs/circ1.html#wccc

How do you secure a copyright?
http://www.loc.gov/copyright/circs/circ1.html#hsc

What is notice of copyright?
http://www.loc.gov/copyright/circs/circ1.html#noc

What works are protected?
http://www.copyright.gov/circs/circ1.html#wwp

What is not protected by copyright?
http://www.loc.gov/copyright/circs/circ1.html#wnp