QUICK FIX 

Use the contraction "it's" in a sentence. It's snowing. If you remove the apostrophe and insert the missing letter "i," does the sentence make sense? Yes, it does! It is snowing. 

Try the same exercise with the possessive "its." The dog held onto its bone. Correct! If you had used the "it's" contraction, the sentence would be nonsense: The dog held onto it is bone. 

WHY IS THIS?

"It's" is a contraction, meaning it's taking two words and contracting them into one, replacing part of the second word with an apostrophe. It's is a contraction for "it is" or "it has." 

"Its" is a possessive word, such as "her" or "his," but for words without gender. Our garden was so lush that we invited our neighbors to harvest its bounty.