learn the rule: its / it's

• its is a possessive adjective, indicating ownership of or association to, someone or something, when the owner has been previously mentioned or is easily identified
• Its sock is green.
• Where is its potato?
• it's is a contraction (combination) of it and is and means it is
• Do you know what it's doing?
• It's stupid.
• The two are not interchangeable.
• Getting it wrong makes you look stupid. And ugly.