A digital certificate, also known as a SSL Server Certificate, enables SSL (Secure Socket Layer encryption) on the web server. SSL protects communications so you can take credit card orders securely and ensure that hackers cannot eavesdrop on you. Any eCommerce company will require you to have SSL before you can use their services.
Thankfully, for most people obtaining a digital certificate is not a problem. For a minimal fee, one can usually use the certificate owned by the web hosting company where your page resides.
If you are a larger company, however, you may want to get your own digital certificate. A certificate costs about $125.00 and can be obtained from Thawte or Verisign.