When you initially install Ubuntu and go to youtube, you realize that you need flash player, but once you go to install it , the adobe website will tell you that you need java. So the first thing you need is Java (obviously). There's two options here, Java that has been developed by Oracle, or free and open-source OpenJDK. The last one is simplest to install, and sufficient for most users' needs. Simply open Software Center, and type java. Select OpenJDK Java 7 Runtime and click install. Same thing with IcedTea Java Web Start.