What does copyright protect?

Copyright, in short

• How you get it: automatically upon creation, with no registration needed to own it.
• The US catch: registration is not a perk, it is the door. For a US work you cannot file an infringement suit until the Copyright Office has actually registered the work. Fourth Estate Public Benefit Corp. v. Wall-Street.com, LLC, 586 U.S. 296 (2019). An application in the post is not enough.
• The other US catch: register within three months of publication, or before the infringement starts, or you forfeit statutory damages and attorney's fees for good (17 U.S.C. §412). Actual damages only, which usually means proving them.
• How long it lasts: typically the author's life + 70 years in the EU, the US and Switzerland. The Berne Convention minimum is life + 50, and a good number of countries stop there.
• Important: it protects the expression, not the idea itself.