Welcome to the inaugural edition of Bevboy's grammar lessons
I remain unconvinced that this will be a viable series, but we will give it a go.
Today I want to discuss two simple words that look very similar but mean totally different things. Those words are "its" and "it's". I see these two words being confused all the time. All the time. Even professional documents and professional writers get these mixed up. I wish I understood why.
It's, 99.9999% of the time, is short for "it is". It is that simple.
Its refers to the possessive of it, which is whatever the subject of whatever you're discussing.
Let's use an example or two.
If you are referring the problems associated with, say, concrete mixing, you could write something along the lines of, "Some of its issues are the fact that concrete is a drab gray, and that it can crumble if you're not careful." You absolutely would not, upon pain of being forced to watch me eat a spaghetti dinner with my toes, write it as, "Some of it's problems are...". You are revealing your ignorance when you write the possessive of "it" as "it's". Just don't. I have a box of pasta at my desk at work, and can cook it any time I want.
Remember when I wrote "99.9999%" above? There is an exception, but it is a silly one, and I hesitate to mention it. I only do so because some wiseacre reading this may bring it up. I'll beat him to the punch.
In the early 1970's there was a comic book called "It! The Living Colossus" about a giant rock statue that becomes animated and wreaks havoc. Good fun for the whole family. Those issues were written by the guy whose message board I quit in 2007, which then led to the creation of this here blog. But I digress.
If you were writing about this character in the sense of describing it or something, you could write along the lines of, "It's torso is 30 feet around. It's arms were 40 feet long." Whatever. In this case only, when the name of a person, place, or thing is "It", then you would have to write "It's" when referring to something which belongs to that person, place or thing.
So, to sum up: it's is short for "it is" some 99.9999% of the time. Its refers to the possessive of some place or thing, 100% of the time.