A noun is a person, place, thing or idea. That is easy enough. However, sometimes plurals and possessives can often confuse even the best reader. For example, “the boys locker room” is one of the possessives ending in s that can cause any writer quite the conundrum.
One way to keep plurals and possessives separate is by turning the sentence into a “of the” construction. Is the final noun a part of the first noun? If so, you must use possessives grammar to write it correctly. For example, “the computers’ screens” could easily read “the screens of the computers.” This phrase indicates there are several screens belonging to several computers. This possessive ending in s makes clear how best to write the apostrophe.
One of the most confusing possessive is the indefinite pronoun “it” and possessives grammar. Most writers want to add an apostrophe, which shows possession of an inanimate object. But that would make the contraction “it is.” That is such a common mistake that many billboards, menus and even a television show printed it incorrectly. The proper form of showing possession for the indefinite pronoun “it” is simply “its.” While this looks wrong, it is quite correct and just another example of how odd and unique is the English language.