Good question and as usual if it matters hire a lawyer
Copyrights usually covers a collective of ideas as assembled into a completed form. For example you can not copyright the word “the” but can as part of a collective of words that makes up a story.
Copyright also covers creative works like paintings and photos so if you take a photo or paint a picture of a chair then you own the copyrights to those images.
What can not be copyrighted is items that are quotidian, common everyday, as to purpose of function. You can not copyright a chair, a table, a car, a bus, a gun, the wheel or anything that has a practical function of the common good aka fair use
You can however copyright the plans of how to make a chair as it’s considered creative works that is unique
The there are trademarks and patents which neither applies unless your making a very unique chair 
P.S. The nature of copyright is it is up to the individual who thinks there rights have been violated to file a claim so the copyright cops will not be kicking down your door…unless it’s Disney
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