This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
basically the "S" of HTTPS adds security and optional authentication mechanisms to the HTTP protocol if needed. The security mechanisms are based on certificates but perhaps you want to take a look into Wikipedia to get more information.