General :: Installing/updating Java RE On Ubuntu?

Linux (Ubuntu) is not providing any updates for Java Runtime Environment! According to what I find on my computer, I have Java build 1.6.0_15-b03. Ubuntu Software Center is indicating 6-15-1 (sun-java6-bin). I have manually downloaded JRE 6u17 and 6u18 from Sun. However, I have not - as yet - attempted to install/update Java myself. First, why isn't Linux providing us end-users with the updates as they are published? I thought that, for the sake of ensuring "STUFF" is up-to-date and SECURITY reasons, that the (or some other place) would be providing updates as they occur. I have just started Ubuntu - my ranking - "kindergarden at best"! I still have not been able get the "handle" on the "command line (codes)" structure and usage. I am so use to the Windows way of installing, updating, and upgrading software that Linux (Ubuntu) is causing quite a bit of consternation; just plain frustrating and confusing! I have been trying, and seeing, so-called instructions of how to install/update Java but there are just too many "assumptions" being interposed by the author(s). I just wish, and want, straight forward, step-by-step instructions in the "how to" department - written in plain language, for the complete novice (brand new to Linux). So, here's my question ... how do I manually update/upgrade (or install) Java RE on Ubuntu? Do I have to remove, add, change anything? I'm sure that there are others in the Linux world that are in need of some straight forward assistance. I want to continue using my Ubuntu and honestly, would like to be more proficient in it's use. But in the meantime.