A Terms and Conditions agreement is where you set the rules and guidelines that your customers must follow in order to access the service you provide as a SaaS app. It acts as a legally binding contract between you and your customers. It lays out the conditions of use for the service, including things like copyright restrictions, rules for interacting with other users on the website/app, and dispute resolution procedures.

Note that there's no practical difference between a Terms and Conditions agreement, a Terms of Use agreement and a Terms of Service agreement aside from the names. It may even be called an End User SaaS Agreement (EUSA). The name isn't as important as the content is.