http is a regular webpage.
It stands for hypertext transfer protocol.
https is a secure webpage.
It stands for hypertext tranfer protocol secure.
Any information sent from a form on a https page will be encrypted so its good for things like credit card numbers.
For a page to be https it MUST have an encryption certificate actived on the server the website is on. Contact your web hosting service or consult a web developer with ecommerce experience for more info.