If you are a Windows power user then you will in all likelihood be quite familiar with the trusty old Task Manager, which lists running applications and processes, as well as gives you the ability to force kill these processes in an attempt to manually control your system’s performance or if you are trying to get your PC stable after a hanged process or application. It also gives you a nice overview of system resources and how they are currently performing as a whole.
Pleasingly, Ubuntu offers a VERY similar tool to its users, and if you are familiar with Windows’ tool, then using this equivalent will be a snap. The application in question is called “System Monitor” and on pre-Unity installations you can find it under the System menu, falling in the Administration submenu. (In Unity, you of course simply search for System Monitor using the Home search tab controlled by that little button at the top right of the screen.)
Ubuntu’s System Monitor is split into 4 tabs, the first giving you system information like installation version plus a hardware overview, the second a list of running processes which you can manage from, the third your system resource utilization (in nifty graphs), and finally a File Systems tab that lists all the available hard drive space available to you.