As for installing stuff on Ubuntu, I'd go with the "Add/Remove Programs" selection on the menu that comes up when you click on the biggish button, bottom left, where the Windows Start button would be.
There -are- multiple ways of installing things on Linux - that's one place where Linux falls behind Windows or Mac. Ubuntu has worked through much of that chaos and provided one good way; but if you go looking for individual packages, such as at the OpenOffice website, you will be led down the path of the other ways that are harder on an Ubuntu system.
The add/remove programs would seem to be great. Here is the problem, in my applications I don't have open office Math or the drawing one. But, in add/remove it says I have them already, so I can't download them.