Run Wubi, insert a password for the new account, and click "install". The installation process from this point is fully automatic. The installation files (700MB) will be downloaded and checked, after which you will be asked to reboot. Do so and select Ubuntu at the boot screen. The installation will continue for another 10-15 minutes and the machine will reboot again. This is it. Now you can select Ubuntu at the boot screen and start using it.
You uninstall it as any other applications. In Windows go to the control panel and select "Add or Remove Programs", then select Wubi/Ubuntu and uninstall it. You can also use the uninstaller that you find in the installation folder.