The Mandates API allows you to create and track mandates for recurring payments. A mandate essentially symbolizes the authorization a customer gave you to recurrently charge their card or bank account.
Implementing the Mandates API is not strictly required to process recurring payments. In basic implementations it suffices to create a customer, do a first payment with the customer, and then charge recurring payments on the customer. A mandate is created automatically for the first payment, and that mandate is automatically used for any consecutive recurring payments.
For a step-by-step guide on charging your customers recurrently, refer to Recurring payments.