Copyright protects the expression of an idea, not the idea itself. So Shakespeare, writing today, couldn't sue "West Side Story" for copyright infringement on "Romeo & Juliet." The idea is borrowed but the expression, and thus the copyright, wouldn't be violated.
Word & WordPerfect are both word processors. But they have different interfaces, different expressions. Yes, there are some functions that work the same. But functional components of the way humans already conventionally work are not protectable.
How do you get copyright? Just fix your expression in some tangible way, physical or electronic. You don't NEED to register officially with the government.
(c), [year], [owner's name].
The simple explanation is that copyright lasts about 100 years....ish. Disney manipulates this to their advantage (lobbying legislators for copyright extensions). Copyright also protects look-and-feel -- any unique expression. This includes fabrics and web pages.
You can register with the copyright office (check copyright.gov for more info), and this basically entitles you to walk into federal court and collect some statutory damages if someone's infringed.
Until software was patentable, copyrights were the main way software was protected. This is still true in some ways and places. Most software houses don't actually file for copyright. The code changes so often, and it would need to be redacted, and also if you suspect a conflict you can file right away on an expedited basis.
How do you enforce copyright? You need to prove:
Access (by malfeasant).
Substantial similarity in the work.
You need to protect yourself against employees & consultants, mostly.