Terms of service
The terms of service are the contract you accept when you create an account: what the platform lets you do, what it may do to your account, and how payments, disputes and closures are handled. Accepting them is usually a single checkbox at sign-up.
Where you see it
The link sits beside that checkbox and in the footer of every page, and you are pointed back to it when an account is suspended, when a refund is refused, or when the document is updated and continued use counts as agreement.
Why it matters
The clauses that affect readers most are the dull ones - grounds for suspension, what a chargeback does to an account, regional restrictions, and what happens to an unused balance when an account closes. Behaviour rules usually sit in a separate guidelines document, so reading one does not cover the other.