Terms and Conditions agreements act as a legal contract between you (the company) who has the website or mobile app and the user who access your website and mobile app.
Having a Terms and Conditions agreement is completely optional. No laws require you to have one. Not even the super-strict and wide-reaching General Data Protection Regulation (GDPR).
It’s up to you to set the rules and guidelines that the user must agree to. You can think of your Terms and Conditions agreement as the legal agreement where you maintain your rights to exclude users from your app in the event that they abuse your app, where you maintain your legal rights against potential app abusers, and so on.
You can use this agreement anywhere, regardless of what platform your business operates on:
Desktop apps usually have an EULA (End-User License Agreement) instead of a Terms and Conditions agreement, but your business can use both. Mobile apps are increasingly using Terms and Conditions along with an EULA if the mobile app has an online service component, i.e. it connects with a server.
In your Terms and Conditions, you can include rules and guidelines on how users can access and use your website and mobile app.