When a site is first set up you will be able to access it using the http:// protocol In order to be able to use the https:// protocol you will require a security certificate.
If you don’t have a security certificate then, if you try to access the site using the https:// protocol then you will probably see an error message.
Try these links to see if this website supports HTTPS
Do I need HTTPS?
From wikipedia…
certificate-authenticated SSL is considered mandatory by all security guidelines whenever a web site hosts confidential information or performs material transactions.
performs material transactions = taking payment
If your site is actually taking payment card information then you should have a security certificate. If you’re just using PayPal then it’s probably not necessary as you don’t deal with any payment details.
hosts confidential information = storing information that needs to be protected
If your website is storing information that you wouldn’t / shouldn’t share then you probably need a security certificate.