Use it as a verb. It means to mix with other substances. Don't you dare adulterate my ketchup with mustard. And keep your jelly out of my peanut butter too. I prefer unadulterated condiments.
Use it's (with the apostrophe) only when you mean "it is" or "it has." For example: It's time to go. (It is time to go.)It's been a long time. (It has been a long time.) Use its (without the...
There are a number of ways you can do this: A compound sentence: I went to the closet, my boots weren't there. Using a quote: When I opened the door, she said, "Wow, it's cold out there". Describing...