The Twitcher is a task switcher to jump between running applications and their windows.

Just tap CTRL TAB quickly to switch between the current and the last application/window. Or press CTRL TAB and hold the CTRL key to go through all running applications by repeatedly hitting TAB or ←/→. If you need to get to a specific window of a program, move to its icon as described and then go through its open windows with the ↑/↓ keys.

It's also possible to invoke the Twitcher with CTRL TAB and then use the mouse to choose the application/window you'll jump to when releasing the CTRL key.