Secure form

This client wants me to create a secure form becase the visitors will be inputting their SSN.

I know how to create a PHP form and input the submitted data into a database. What I don’t know is how to make the form secure (https?).

I have my Webhosting with MediaTemple and the control panel states:

Pre-configured SSL:
Your service comes with two pre-configured SSL-capable web addresses.
Both use the same certificate, so there will be a certificate warning on your primary domain, however both are equally protected.
Certificate Signing Request:
To generate a new Certificate Signing Request (CSR) to submit to a Certificate Authority (CA), select ‘generate csr’.

How would I make the data submitted in the form secure? :h: