SSL certificates are what make secure data transfer possible. They are certificates that are installed where a website is hosted so websites can send and retrieve data securely encrypted. There are many different types of certificates with different levels of security and validation, as well as different levels of coverage in the event of trouble. SSL certificates can be purchased through many different providers. Some can charge higher prices than others for similar certificates because of brand, but brand doesn't determine the level of security for you or your customer.
(more about level of security)

Security consists of a few things:
- validation: How much proof of identity is required to get the certificate
    More complete validation = more assurance to the customer
- encryption: How much encryption is used to make the data safe
    Most use 256 bit encryption - cheap ones use 128 bit - EV SSL uses next generation 2048 bit
- warranty level: Level of security to the end user to the validity of the site
    This is Comodo's guarantee that identity was validated
- website identity: What a visitor can find out about the true identity of the website
    A good certificate gives visitors the ability to see for themselves the website is real

Some of the cheaper SSL certificates don't require any validation. That makes them very affordable, but if a visitor decides to view the certificate data, they won't feel very comfortable sending sensitive data. Any serious business should only use a certificate that requires some form of proof of identity. InstantSSL, InstantSSL Pro, and PremiumSSL all require basic proof of identity and of domain ownership. The EV SSL requires full validation, which with newer browsers, gives a green address bar. This provides visual assurance that the website has been verified and is secure.

E-commerce sites NEED SSL certificates