Firstly, I am assuming that the motivation of your question is to install packages, so correct me if I'm wrong.
To run commands a root, you can either execute the commands as the root user, or you can append
sudo to the beginning of the command. For most applications, using
sudo is safer that being root because, among other things, it will force you to make sure that you know what you're doing.
To become root, you can use
sudo -i as Michael has commented below, but that shouldn't be necessary to install Google Chrome. To do this, you can simply enter
sudo apt-get install google-chrome
into the command line, but if I understand correctly, you either don't have the password or something is messed up that prevents you from using
Since you just got Ubuntu, and presumably haven't made any significant changes, you could try reinstalling from the live CD/USB. During the process, there is a prompt to set a password for the account, which you should definitely do -- this will be the password that you will use when using
sudo. No doubt, this will be the easiest way to set up an admin account.
If that doesn't work for some reason, or if you are don't want to reinstall, you will probably have to provide more information to get decent answers. You should be able to see what type of account you have (admin or not), and that will tell you if you have
sudo permission in the first place.