Common items in a terms and conditions agreement allow you to:

• There are no refunds after the materials have been sent to the customer. 
• Manage customer expectations, such as liability for information errors or website downtime.
• Explain your copyright rules, such as attribution, adaptation, commercial or non-commercial use, etc.  See Client Bill of Rights. 
• Set rules for user behavior, like forbidding unlawful behavior, hate speech, bullying, promotions, spam, etc. See Client Bill of Rights.