The activities overview is the screen that's displayed when you click the Activities button at the top left of the screen.

When you hold down the Alt key and then press Tab, a window switcher appears. This shows a list of the windows you have open, with a preview and the name of the currently-selected window.

The dash is the list of your favorite applications that is shown on the left-hand side of the activities overview. This is sometimes referred to as the dock.

The hot corner is the corner at the top left of the screen. When you move the pointer there, the activities overview opens.

Notifications are messages that pop-up at the bottom of the screen, telling you that something just happened. For example, when someone chatting with you sends a message, a notification will pop-up to tell you.

The System Settings are where you can change preferences and so on, similar to the Control Panel in Windows or the System Preferences in Mac OS. Click your name on the top-right of the top bar and select System Settings to access them.

The top bar is the bar that runs along the very top of the screen. The Activities button is on one end of the top bar and your user name is on the other.

You can put windows on different workspaces. They are a convenient way of grouping and separating windows.

The workspace switcher is the list of workspaces that is shown on the right-hand side of the Windows view in the activities overview.