Copyright protects an expression whether that be in words or an "artistic" endeavor, 2-D or 3-D, static or performance. It does not protect the ideas expressed. You can write a love story but so can anyone else. You can sculpt a rose but so can anyone else. And, as far as copyright is concerned, if someone else's love story or sculpted rose comes out identical to yours, or nearly so, they are just as much entitled to the copyright on theirs as you are on yours. The key is independent creation. COPYright is a right that you can use to block others from copying you more or less identically. There are also some limitations on derivative works but to violate your copyright such a work done by another would pretty clearly have to be derived from your work, not just from the idea behind it.
As far as use of copyright for inventing goes you cannot copyright your invention or its idea but you can "copyright" your commercials, advertising, package printing, instruction sheets, manuals, etc. Technically you actually own the copyright on each of the "works" mentioned in the previous sentence the instant the work is "fixed in a tangible form" and you own the copyright--even if you don't provide notice or register your copyright. Even when you write a patent application you own the copyright on your patent application after you've finished writing it BUT, you give your copyright in the application up as part of the bargain to get a patent issued. In some instances the courts may allow you to enforce a copyright on perhaps specific drawings and in specific contexts for parts of your patents but the general rule is anyone can freely copy your patent (the text and drawings of the patent document itself, not the claimed invention) or any part of it for patent related purposes.
If you retain an independent individual, or ad agency, etc., to create materials be certain your contract or agreement (in writing) spells out that the materials created for you are "works for hire" and that you retain the copyright. Failure to make clear in writing that the work is being made for you "for hire" will leave the copyright legally in the hands of the creator of the work. Depending on what contribution you made to the work you may also have copyright rights in the work and therefore the right to authorize copies yourself but it is still best to have a written agreement with any contractors or outside help spelling out your ownership. If actual employment records show the creator is an employee of you and directly or indirectly acting under your direction to create the work then you don't need a written agreement that shows you own the copyright because the law allows for that--but a written agreement won't hurt either.
To publicly declare your copyright (i.e., "give notice") all you need to do is place the word "Copyright" or the c-in-a-circle "©" symbol (or both)--"(C)" i.e., a c-in-parentheses, is NOT valid--followed by the year of first publication and a generally recognizable form of your name or DBA or corporate name. It also won't hurt, but it is not required, that you include "All rights reserved." The "All Rights Reserved" used to be important (but probably isn't any more) for full foreign coverage and where alternate media might be used such as a movie from a novel.
Revised versions of your works should have the correct new year of publication in their copyright notice, not (just) the year of the unrevised original version.
To "perfect" your copyright on a specific item you must register your copyright with the Library of Congress Copyright Office (loc.gov or specifically copyright.gov). Each copyright registration with the Library of Congress requires completion of a form, a payment for $35 or $65 (subject, of course, to change), and usually 1 (rare) or 2 (almost always for printed or published material) copies of the material being registered. See copyright.gov/eco/ for details. It may take you a while to dig out the information you need but it is all there at the Internet site. Also be aware that for the fullest copyright protection you must register within 3 months of your work's publication.
A U.S. Copyright is recognized by over 190 countries including most that are likely to provide viable economic markets for you so you only have to register your copyright and pay the fee once for each item. For an individual the copyright is good from the moment the work is in "tangible form" through 70 years after the death of the individual. For a "work made for hire" or with no identified human author either in the work or its registration, usually for a company, the copyright is good for the lesser of 95 years from first publication or 120 years from creation.
Failure to provide a copyright notice with publication, especially if it can be shown that the failure was not accidental or that, even if it was accidental, no attempt was made to correct it, can completely invalidate your copyright so be very careful. If your copyright is not filed with the Library of Congress the United States will refuse to become involved in any disputes arising out of your copyright claim. If your copyright is filed with the Library of Congress the United States will "lend its support" to your case (but it won't make it for you or pay any expenses) and you may be eligible for treble damages should you prevail. Customs intervention may also be possible. In my opinion, the fee is well worth it.
Relative to your product, the most valuable place for copyrighting is probably on instructions that are provided with the product. It is far more likely for a knockoff artist to copy those (or to try to get away with a "derivative" version of them) than to copy your packaging unless they are fraudulently attempting to sell their product as yours.