PayPal Recurring Payments allows you to bill a buyer for a 
fixed amount of money on a fixed schedule. The buyer signs 
up for recurring payments during checkout from your site. 
Consider the following examples: 

A buyer purchases a subscription to a magazine or 
newsletter from your site and agrees to pay a monthly fee. 
A buyer agrees to pay an Internet Service Provider a flat 
fee on a semi-annual basis to host a website. 
These examples represent payment transactions that reoccur 
periodically and are for a fixed amount.
When you create recurring payments for a buyer, you create 
a recurring payments profile. The profile contains 
information about the recurring payments, including details 
for an optional trial period and a regular payment period. 
Each of these subscription periods contains information 
about the payment frequency and payment amounts, including 
shipping and tax, if applicable.

After a profile is created, PayPal automatically queues 
payments based on the billing start date, billing 
frequency, and billing amount, until the profile expires or 
is canceled by the merchant. The buyer can also cancel the 
recurring payment profile for profiles creating using 
Express Checkout.

Note that for profiles created using Express Checkout, the 
queued payments are funded using the normal funding source 
hierarchy within the buyer's PayPal account.

After the recurring payments profile is created, you can 
view recurring payments details or cancel the recurring 
payments profile from your PayPal account.You can also 
access recurring payments reports from the PayPal Business 
Overview page. 
More information about recurring payment is available at
https://www.paypal.com/IntegrationCenter/ic_recurringpayment
s.html