How to Setup for Recurring Giving
The answer depends on your payment processor, but here's the general plan:

Contact your payment processor and inform them that you want ARB (Automated Recurring Billing) added to your account. Most payment processors will add an additional monthly charge (around $10-20/month). Some (like iATS Payments) do not.
Most payment processors (e.g. Authorize.Net, PayPal) will send a notification to a predetermined URL when they process a payment.  Instructions are here for PayPal and Authorize.
Other payment processors (e.g. iATS Payments) store a token in CiviCRM.  CiviCRM submits the token on a regular basis to process a payment.
On any contribution page, go to the Configure menu &gt; Contribution Amounts and check the box labeled &quot;Recurring Contributions&quot;.

You can configure your options from there.  Bi-monthly and quarterly transactions are possible by specifying recurring intervals.  I've been commissioned to write an extension to add &quot;quarterly&quot; as an option without using intervals, but it's not written yet!