The "admin" is disabled by default (i.e. root) In Ubuntu. To run administrative tasks from the command line you will have to use "sudo" (e.g. sudo apt-get install mplayer
If you are using the GUI (and since you've said you are a "noob"; I'm sure you're using the GUI...nothing wrong with that); it will automatically ask you for your password every time you want to do an administrative task.
Google has some good information ( www.google.com/linux
); try searching from there (remeber the "/linux" when you type google.com
If you are really interested in Ubuntu (and Linux in General) you can take a look at books for Ubuntu...
Some will argue with me saying that "you shouldn't learn with ubuntu"...But I think it's a good "beginner's distro"; Have Fun
Something to think about
: You won't have good experience installing it through VMWare