SSL (Secure Sockets Layer) is a cryptographic protocol to provide a secure (encrypted) channel between two computers over the internet (or local network). This ensures only the intended party (web server) can read the sent data.
Sensitive data passed from Your machine over the internet to the destination server can become readable to hackers without a secure SSL connection. SSL provides authentication, trust and is required for PCI compliance.
SSL enabled websites run on https instead of http as 'S' stands for secure. A valid SSL certificate is indicated by a green padlock in the browser's URL. Chrome marks websites without a valid SSL certificated Not Secure.
The Car Advertiser always runs on https.