An SSL certificate allows a website to have a secure page where any information submitted on that page will be encrypted. A common use of this is on checkout pages where people are putting their credit card information in to make a purchase. SSL prevents other users from stealing your credit card information when you put it into the site.
However, a site must both have https enabled in front the url you’re on, in addition to having a verified SSL certificate, in order for that page to be protected. If you see a web page without https in front of it, that means the page is unprotected and any information you send could be stolen by another person when you submit it. Your browser will likely have an icon next to the url, such as a shield, that further lets you know the page is secure. Examples:
Unprotected page: http://www.powerupproductions.tv
Protected page: https://www.powerupproductions.tv/checkout