Each time you visit a website your browser remembers / stores parts of the website so it can load the page faster next time you visit that website. This is called Caching. Sometimes caching can prevent you from seeing the latest version of the website e.g. new images / content that have been added since the last time you visited.
Google Chrome's security lead and engineering director, Justin Schuh, has warned that users of the most popular web browser should update "like right this minute." Why the urgency? Simply put, there is a zero-day vulnerability for Chrome that the Google Threat Analysis Group has determined is being actively exploited in the wild.
An SSL Certificate (Secure Sockets Layer) creates a secure link between a website and your internet browser. The SSL Certificate ensures that all data passed between the two is encrypted and stays private, this helps prevent hackers from stealing your private information such as credit card numbers, names, address and other sensitive data.